Dear Johnny,
1) GR/IR should not be allowed to post manual.Since it should be marked as " post automatically only" in GL master
2) In case you are allowed to post few manual entries then check the same in T.code FAGLL03 by differentiating document type ie..GR - WE , IR - RE & manual as SA etc...
Hope this information will help you.
Regards,
L.Ananthakrishnan