HTTP request validation Exception in ASP.NET Web Service on Ubuntu with Mono

First of all I am totally new to Linux Os and Mono as well.

I have taken all the steps from the following post to run my Web API service with Mono on Linux Ubuntu:

http://piotrwalat.net/running-asp-net-web-api-services-under-linux-and-os-x/

Now I am able to run my Web service on Ubuntu from localhost:5757, but when I execute a method, I get System.Web.HttpRequestValidationException:

A potentially dangerous Request.QueryString value was detected from the client 

This is my test method:

[WebMethod]
public string Test(string strXML)
{
    string strMessage = "";
    XmlDocument xdoc = new XmlDocument();
    try
    {
        xdoc.LoadXml(strXML);

        XmlNode xContent = xdoc.GetElementsByTagName("content")[0];
        strMessage = xContent.InnerText;
    }
    catch (Exception ex)
    {
        csGlobal.ErrorLog(ex.Message + " " + ex.StackTrace);
    }

    return strMessage;
}

This is the Input XML message that I want to test:

<data><content>some content</content></data>

It works perfect in IIS with Windows. But how can I make it work with Mono on Linux?

UPDATE:

.NET version is 3.5 and I added <pages validateRequest="false" /> in my web.config file, but still getting the same error.

What do you suggest me to do???

Change your Web API's .Net Framework version to 4.0 and include the following in your web.config:

<httpRuntime requestValidationMode="2.0"/>

This should help. But please note that in this case your API will be less protected and less stable for outer attacks.