APP-F110 not picking the SA document type

Dear Guru's

we a case where users are posting vendor related transactions some times using SA document type....but during F110 execution system is not picking the SA document type and issuing error message but clearing KR and RE document types...

Before posing this issue i verified in our system no. of times but still i'm receiving the same error....so request you plz give some inputs to over come this issue.

Regards,

balusiva.