Error in Posting of Foreign Currency

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Hi,
I am trying to post foreign currency but i keep having the error below:

The transaction cannot be completed because it will cause inconsistencies in the G/L Entry table. Check where and how the CONSISTENT Function is used in the transaction to find the reason for the error.
Contact your systems manager if you need assistance.
Parts of the program mark tables as inconsistent during very comprehensive tasks, such as posting. this prevents data from being updated incorrectly.

I go to Periodic Activities->Finance Charge Memos. under Issuing bottons i click on issue finance charge Memo and say OK. It gives the above error.
How can i solve this? can someone help me please.
Thanks