i haven't seen this issue, but in general when you get errors of the form "<someclass> is ambiguous in the namespace...", it indicates one of the following problems

• you have 2 instances of the same class in the application space. This usual happens when either
  • you have 2 different file names for the same class e.g. dotnetnuke.dll and dotnetnuke.bak.dll (perhaps an old version you decide to rename rather than delete)
  • you have the same class in 2 locations e.g. in the bin folder and the app_code folder
• you are running your website in an app pool that has 2 versions of the framework running (in theory this is not possible, but i've read of instances where a crashed 1.1 version in the pool infected a working 2.0 install). To fix this unload the application pool.
• in asp.net 1.1, from time to time this error occurred when an old temporary file remained in the temp folder (i.e. C:\WINNT\Microsoft.NET\Framework\v1.1.4322\Temporary ASP.NET Files . You could try clearing out this folder and seeing if this helps.

Cathal