How can I see to it that my WebPart is found and registered as safe?

In debugging my WebPart to see why its controls are not displaying, I put the page in edit mode in the browser to first remove all the superfluous instances of the WebPart so that I would step through the CreateChildControls() etc. methods only once.

On doing so, though (putting the page into Edit mode), I saw that each WebPart contained the following err msg:

Web Part Error: A Web Part or Web Form Control on this Page cannot be displayed or imported. The type WebFormPDFGen.WebFormPDFGenWebPart.WebFormPDFGenWebPart, WebFormPDFGen, Version=1.0.0.0, Culture=neutral, PublicKeyToken=42314blabla could not be found or it is not registered as safe.

What? WebFormPDFGen.WebFormPDFGenWebPart.WebFormPDFGenWebPart is not found? The solution name is WebFormPDFGen, the WebPart is named WebFormPDFGenWebPart, and so are the .cs and .webpart files:

WebFormPDFGenWebPart.webpart does contain a reference to the unfindable entity (WebFormPDFGen.WebFormPDFGenWebPart.WebFormPDFGenWebPart):

<?xml version="1.0" encoding="utf-8"?>
<webParts>
  <webPart xmlns="http://schemas.microsoft.com/WebPart/v3">
    <metaData>
      <type name="WebFormPDFGen.WebFormPDFGenWebPart.WebFormPDFGenWebPart, $SharePoint.Project.AssemblyFullName$" />
      <importErrorMessage>$Resources:core,ImportErrorMessage;</importErrorMessage>
    </metaData>
    <data>
      <properties>
        <property name="Title" type="string">WebFormPDFGenWebPart</property>
        <property name="Description" type="string">My WebPart</property>
      </properties>
    </data>
  </webPart>
</webParts>

So...is it that the webpart is not registered as safe, as the second part of the err msg mentions? What do I need to do to register it as safe?

UPDATE

I get the same issue at runtime with a very basic WebPart based on the walkthrough here:

When I add the WebPart to my test page, it renders fine - it has the expected "Hello, world!" message based on the code from that walkthrough, which is simply:

[ToolboxItemAttribute(false)]
public class XMLToPDFWebPart : WebPart
{
    private string customMessage = "Hello, world!";

    [WebBrowsable(true),
     WebDescription("Displays a custom message"),
     WebDisplayName("Display Message"),
     Personalizable(PersonalizationScope.User)]
    public string DisplayMessage
    {
        get { return customMessage; }
        set { customMessage = value; }
    }

    protected override void CreateChildControls()
    {
        base.CreateChildControls();
        LiteralControl message = new LiteralControl();
        message.Text = DisplayMessage;
        Controls.Add(message);
    }

...but when I subsequently view the page when running the other project/WebPart, it not only no longer cheerily chirps, "Hello, world!" but it blasts the following foghorn in my face:

Web Part Error: A Web Part or Web Form Control on this Page cannot be displayed or imported. The type XMLToPDF.XMLToPDFWebPart.XMLToPDFWebPart, XMLToPDF, Version=1.0.0.0, Culture=neutral, PublicKeyToken=42f314BleeBlahBloo could not be found or it is not registered as safe.

Why does it now decide that the WebPart is lost or unsafe, when it displayed it before?

UPDATE 2

I got an err msg with a correlation number when selecting and 2-clicking the simple WebPart in the WebPart Gallery. These are the lines in the Log file that contain that correlation number:

03/24/2015 13:33:21.37  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           Logging Correlation Data        xmnv    Medium      Name=Request (GET:https://duckbilled.platypus.poisontoe:443/_layouts/WPPrevw.aspx?ID=208)   05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.39  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           Logging Correlation Data        xmnv    Medium      Site=/  05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.43  w3wp.exe (0x1980)                           0x0320  Document Management Server      Document Management             cm6w    Medium      Template Discovery/InitScriptData: cannot get user profile, no UserProfileApplicationProxy exists in the current context    05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.43  w3wp.exe (0x1980)                           0x0320  Document Management Server      Document Management             cm6w    Medium      Template Discovery/InitScriptData: cannot get user profile, no UserProfileApplicationProxy exists in the current context    05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.45  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           Monitoring                      b4ly    High        Leaving Monitored Scope (EnsureListItemsData). Execution Time=11.0956839486583  05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.46  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           General                         avro    High        Relying on fallback logic in VghostPageManager::getGhostDocument() for document: 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\Template\Features\XMLToPDF_Feature1\XMLToPDFWebPart\XMLToPDFWebPart.webpart'  05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.46  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           General                         avro    High        Relying on fallback logic in VghostPageManager::getGhostDocument() for document: 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\Template\Features\XMLToPDF_Feature1\XMLToPDFWebPart\XMLToPDFWebPart.webpart'  05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.46  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           General                         avro    High        Relying on fallback logic in VghostPageManager::getGhostDocument() for document: 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\60\Template\Features\XMLToPDF_Feature1\XMLToPDFWebPart\XMLToPDFWebPart.webpart'  05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.46  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           General                         avro    High        Relying on fallback logic in VghostPageManager::getGhostDocument() for document: 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\Template\Features\XMLToPDF_Feature1\XMLToPDFWebPart\XMLToPDFWebPart.webpart'  05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.46  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           General                         avro    High        Relying on fallback logic in VghostPageManager::getGhostDocument() for document: 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\Template\Features\XMLToPDF_Feature1\XMLToPDFWebPart\XMLToPDFWebPart.webpart'  05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.46  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           General                         avro    High        Relying on fallback logic in VghostPageManager::getGhostDocument() for document: 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\60\Template\Features\XMLToPDF_Feature1\XMLToPDFWebPart\XMLToPDFWebPart.webpart'  05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.46  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           General                         8kh7    High        Cannot complete this action.  Please try again. 05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.46  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           General                         8e2s    Medium      Unknown SPRequest error occurred. More information: 0x80070002  05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.47  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           Runtime                         tkau    Unexpected  Microsoft.SharePoint.SPException: An error occurred when previewing the Web Part.    at Microsoft.SharePoint.WebPartPages.WebPartPreview.CreateChildControls()     at System.Web.UI.Control.EnsureChildControls()     at System.Web.UI.Control.PreRenderRecursiveInternal()     at System.Web.UI.Control.PreRenderRecursiveInternal()     at System.Web.UI.Control.PreRenderRecursiveInternal()     at System.Web.UI.Control.PreRenderRecursiveInternal()     at System.Web.UI.Control.PreRenderRecursiveInternal()     at System.Web.UI.Control.PreRenderRecursiveInternal()     at System.Web.UI.Control.PreRenderRecursiveInternal()     at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)   05556c29-2d56-4093-9a6a-15ed2346f3db
03/24/2015 13:33:21.57  w3wp.exe (0x1980)                           0x0320  SharePoint Foundation           Monitoring                      b4ly    Medium      Leaving Monitored Scope (Request (GET:https://duckbilled.platypus.poisontoe:443/_layouts/WPPrevw.aspx?ID=208)). Execution Time=208.394083605598 05556c29-2d56-4093-9a6a-15ed2346f3db

Note that if I try to add that WebPart to a page now, it tells me, "The operation could not be completed because the item was removed from the gallery"

UPDATE 3

Cleaning, rebuilding, and [re-]deploying seems to at least temporarily fix the new, super-simple WebPart:

...but my level of confidence that it will not become WebPart-non-grata is not exactly approaching Everest heights - maybe Mt. Timm.

As you can see, though, the original WebPart is still heaving an error.

What I would advise is downloading an add-in for visual studio. It's called CKSDev tools

What this allows you to do is package your SharePoint solution in to a WSP and then deploy the package and this should take care of your safe controls.

CKSDEV tools

This will help you with debugging and is generally awesome when it comes to SharePoint development. They even have thrown in a few templates for stuff like site templates which will save you oodles of time.

You may have to create a new SharePoint project and migrate your code but once you've got CKSDev working you should be golden.

The other option is to locate the web.config of your web app and add a safe control with the assemblies your solution is moaning about but I wouldn't do this because you will get the same issue when moving it to production and when you start playing around with those files it's easy to make mistakes which can cause you more pain.

Cheers

Truez