The type 'xxxx' exists in both '...\v2.0.50727\Temporary\....xxx.dll' and '...\v2.0.50727\Temporary\...yyy.dll' Location: BlogsMäx's blog Posted by: m.unterauer 01.03.2006 This error occurs, if you have declared a class twice in your application (in a referenced assembly, somewhere in your app_code directory, or anywhere else in your app).In my case I had a prior compiled version (a dll) of the web app itself in the bin directory, which is not allowed any more. -> delete all compiled versions of all web applications (the app itself and referenced web apps) from the bin directory !!If you have to have the same classname multiple times within your application (e.g a class "DataAccess" within each module subfolder in the app_code directory, you could do the following:1) Give each class a different namespace (e.g. MODULENAME.DataAccess)2) Mark the classes as partial classes (!! this does not work if the partial classes are spread accross different subfolders of the app_code dir which are marked as codeSubDirectory in the web.config. The reason is, that in this case, each subfolder results in a different assembly and partial classes over multiple assemblies are not allowed. Also see my blog entry for creating multiple assemblies from the app_code directory !!)