Hi Veena
Sometimes when we do a RFC call check what is the value you are passing for example if the field is char10 and you are passing 8 digits then it will add junk charcter in the end and hence no data would be fetched ..
So if you use a conversion routine the issue should be fixed .. if you have the PO number is not 10 digit try using this logic ..
else check if you are able to debug and see what is the value coming in the production in backend
Try replicating the issue in Dev system if your are using this as soon as the document gets created it is possible that the value has not been updated
Also you can pass COMMIT and WAIT statement or call FM in update task to cause some forced delay
Regards
Vinita