I have tried to clean and rebuild the solution but no avail.
It happens even with a new blank website I created after your reply.
I think it is probably because the DotNetGallery.dll was built either with older version of Visual Studio or with some build settings that is not compatible with Visual Studio 2008 version with .Net 3.5.
Do you have an older version of the dll that I can download?
Thanks,
jmash