Cost center is blocked against revenue posting.

Hi FICO Gurus,

while doing FB50(Commission A/c-- DR,1000...To Special Discount 1000),after filling the relevant Cost center for Both the GL,system is saying that

Cost center is blocked against revenue posting so & so date...later on i checked  both the GL & cost element(1-Primary costs/cost-reducing revenues,and for Special Discount GL 12 Sales deduction)

                                                                                 After that i went to KS02 & unchecked the Actual revenue in contol tab. But i m getting the same.

Pls give ur valuable comment.

Thanx.

Amit