George,

I still could not replicate those error in my environment.
Could you let me know your environment detail?
Also, please try to remove asp.net cache at C:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files. 

Regards,
Handy

Windows7
VS2008

I used the same environment as yours. Is it 64 bit machine? If it is possible, please send me a recording video about it. Maybe something i did wrong in replicating your issue.

Regards,
Handy

Handy, apparently, this only happens in the existing project.  In a new project, it works fine!

I still could not see the error. Can you reproduce within WebTreeView sample project?
If it is under existing project, please ensure you have use the latest assemblies of WebTreeView in your project bin folder.

Regards,
Handy

Here is the Video

In your video,  I noticed that you replicated it inside WebUserControl. I did not test it with that format. I will let you know asap.

Regards,
Handy