>>SourceMedi has an index, but it's not the primary key.
>>
>>I don't see how this problem can be related to the fact that it is a primary key or not. It work for every other SourceMedi value except the blank one.
>>
>>>Is SourceMedi an index key in the source table? If not, that's your problem.
>
>
>I'm going to create a mockup of the problem and post a better answer :) Gimme a bit.

I have been unable to duplicate the problem...can you post the exact source table structure and list of all table indexes?