Invalid column name when transfer from uneven sources

Hi all, I have not been able to find any similar posts.

My problem is that I stumble over an execution error when trying to map two different sources with identical columns, except one, that only exist in one source. I except data from one of the sources into the column and expect Null from the other on the lines originating from the other.

But however Timextender throws error "Invalid column name 'XXXXX' " on the column at execution. Have tried full deploy. Only if I remove the XXXXX column it will execute.

Any ideas?