Ok - it was my fault. The a6mysql.dll works fine now. I just tried it without the mysql Libs available. After installing mysql on my computer, the dll could be loaded without problems.
I installed the whole server - not sure, which DLLs are needed to use that DLL.
Hope that helps a little.
(But then I still don't know, why my DLL couldn't be loaded.)
Konrad
Edit: I should test more before posting
You need the libmysql.dll! Just copy it into your project. Then you should be able to load the a6mysql.dll.