That was the clue i was looking for.

Just before i saw your reply i tested edit order 1.5.3. on zencart 1.39e and there everything worked.
Since 1.39e many extra's are added to this init_sessions and the edit orders now falls in this if structure preventing it from working.
As far as i can see there is no problem adding this extra file to the line and after that everything works fine.
Maybe drByte can confirm this if he has some time left.

Thanks a lot for the hint