In delphi, creating ActiveX controls was something that was once more popular than it is now. However it remains possible to create ActiveX controls with Delphi. This question assumes Delphi 2007, but it should be the same no matter what Delphi version you use.
There are some strange errors in Delphi when you create ActiveX controls. IN my case, I can now no longer import a certain class that I am trying to import and wrap, and Delphi won't tell me why any more, just that it could not load the unit "symbol information".
In this case, I am wrapping an open source control, and my first few attempts to wrap it worked fine, but I found that I had to redo the import once I found properties that were written in a way that the ActiveX wrappers were missed. It's easier to regenerate an ActiveX wrapper than to fix it by hand. Until you get stopped cold like this:
Error
Could not load unit [unit] symbol information for [TClassName].
Do you want to try to find this file yourself?
If I click Yes, I get a browse (file open) dialog and it has the file filter set to "DCU". Which means, it wants me to find the DCU file for this unit. If I browse to it, or if I don't, the results are the same. No amount of recompiling will clear this error condition.
does anyone know what this error really means, and better yet, how to fix it? Googling this particular error message shows it comes up in forums other than English, but is so obscure nobody has yet documented it.
There is an issue with the Library Path in Delphi, that for the ActiveX Control wizard to work properly, all sources needed for the parser to parse the unit in question must be in the library path. Since the ActiveX control wizard functions outside your project, your project search paths are NOT included in the list of folders that are used to parse the sources of the VCL control that is to be wrapped and turned into an ActiveX Control.
Solution:
Fix the library path.