A simple, yet common source of errors is ASP.NET Version mismatch. Make sure that your ASP.NET version 2.0 DLL is on a site that has this same dot net version enabled.
If you have uploaded the DLL via FTP, this is probably the cause. A DLL usually needs to be published via Visual Studio or similar tool and in the process it needs to recompile. This will not normally occur if you upload with FTP.
Other causes can include assembly, object or other references found in your local environment but not on the server. The servers run the .NET run time environment only, if your application relies on components not found in the run-time, it will not work as expected.
Attempt to republish the site so that the DLL is recompiled and loaded to the server. If you see errors or other misbehavior, verify the code trying to execute is valid for the server.
It may also be helpful to upload the source only to help assist in determining the exact cause of the failure. We cannot easily debug DLL files, as we cannot see the source nor make modifications for testing. In addition, programming falls outside the scope of our free technical support mandate; however, programming support is available for a fee. Send an inquiry to: firstname.lastname@example.org for more information on Alentus Programming Support.