Credit Memos in error "Invoice Cannot Be Credited Due To Its Electronic Invoice Status""

There are lot of Credit Memos in AR interface lying with error "Invoice Cannot Be Credited Due To Its Electronic Invoice Status". Below is the suggestion from a previous note in metalink"The only way to cancel the locked transaction is to apply a credit memo that has a transaction type of VOID.  Also the amount of the Credit Memo must match the amount of the Invoice to be credited. However, as shown by the error above, such a credit memo could not be imported due to the raised error."
We tried by associating the credit memos to a void transaction type but it did not work.