What happens when you change the status directly through transaction instead of function module? Do you get any error message there? Please also check if following link helps:
http://scn.sap.com/thread/1882185
Regards
What happens when you change the status directly through transaction instead of function module? Do you get any error message there? Please also check if following link helps:
http://scn.sap.com/thread/1882185
Regards