Idoc File TO Idoc-XML conversion via RSEINB00 throws an error

Hi Experts,

I have a scenario where i am picking a flat file(representation of an Idoc) from a 3rd party system and putting it into Integration Server via File Tunneling.From the IS i am running the program RSEINB00 with the file which was picked in order to convert it into Idoc-XML format. But when i run the program with the picked up file the program gives an error "The file has not been accepted for processing". Is there any modifications to be done to the file before running the program....I assume there must be some changes to be done in the control record. Please let me know...

Thanks in advance,