not able to post the invoice cancel MR8M document

Dear All,

I am not able to cancell the invoice document using MR8M transaction. System is showing the message as "balance not zero, difference between debits & credits"

Invoice document is created in the FY 2006 as a credit memo, and now i want to reverse/ cancel it by using MR8M transaction.

Pl. let me know the possibilities & checks required for cancellation of it.

Regards

Mangesh