GL Account Balance is not matching with AP Trial Balance

Dear All,

Although I'm following the Oracle recommended payables reconciliation method which is:

Last Months Accounts Payable Trial Balance 

+ This months Payables Posted Invoice Register 

- This months Payables Posted Payment Register 

= This months Accounts Payable Trial Balance

But AP TB balance is not equal to GL account balance (as per Account Analysis Report and GL account inquiry). Kindly let me know what could be the reasons behind the difference amount.

NOTE: All transactions has been transferred and posted into GL and periods has been closed from both GL and AP.

Thanks

Syed Ehsan