Ok, but is this update done via a custom script where I create a dataadapter. Because I already implemented this and I was wondering if this is the most simple...

Yep. This also a solution.

Tnx again.

I found the problem and it is a bug

I'm sorry but don't understand what you mean.

I have changed in the Parameter Mapping section the row with

User::ImageKey, ReturnValue, Numeric, 0

But still it doesn't work.