Back in October I posted about how you can enable your applications to work well with UAC. Whilst the solution I presented for Visual Studio 2005 works quite well, allowing you to run and debug your application whilst still using delay signing to incorporate the manifest files, it does have a significant drawback.  Unfortunately the visual designer in Visual Studio 2005 appears to use an intermediary build of your assemblies in order to resolve class references.  This means that it is using the assemblies prior to them being signed and thus failing validation.  The result is that the visual designer fails to resolve class references giving you something similar to the following error.

The question is what do can you do to fix it? Well firstly, don’t spend hours rebuilding your project or upgrading to Visual Studio 2008 in the vain hope it will fix it!  That’s what I did and am now kicking myself that I’ve had to waste so long tracking this down.  The only solution I’ve found is to simply disable the delay signing and REM out the post-build actions you created to embed the manifest file.  Of course, you then need to remember to add these back in when you have finished doing the work with the designer.

Note: This only seems to be an issue where you are using visual inheritance to controls/forms that are in the delay-signed assembly.