Hi Emad,
"The error cash discount may be granted up to 0 % " is because in the invoice 3 % cash discount is given, however the user(you) is not granted the privilege to provide discount. To solve this issue go to (oba4) and feed in detials and save it.
Also check the following
Employee tolerance –
oba4 (FI tol group for users),
ob57(assign user's tol group)
Master data tolerance
A) G/L a/c tolerance –oba0
B) Customer/Vendor tolerance-oba3
Good luck !
Regards,
Sam