First record is not an IDOC control record - Error

When I am trying to import orders in my test system through RSEINB00 , it is giving me this error "First record is not an IDOC control record"

But if I manually do it through test tool , it post successfully.

I tried different files which have been posted into production client successfully but still the same error.

It was working just fine until yesterday. Today I modified one file and ran it and it gave me the error. Now its giving me the error in all the file i try.

Any clues ??