I got this error in one of my ASP.NET web sites after uploading a new version:

BC30560: ‘MySqlConnection’ is ambiguous in the namespace ‘MySql.Data.MySqlClient’.

It worked fine on my development machine but not on the production server. I could not figure out what it was for quite some time. Turned out I had added the mysql.dll to bin directory of my project and at the same time was referencing a shared (GAC) version of the same dll. I had made this and some other changes on the development machine that I had forgot about. The only thing that differed from the development and production machines was the web.config which I obviously did not check well enough.

Posting this here if someonelse or myself makes this stupid mistake again…