Invoice is created but journal entry is not posted to GL. 

In this case, which happens only rarely (usually due to a hardware or a power failure), an AP record has been entered, and exists in the system, but the general ledger was not updated as the invoice record was saved.  This type of error is usually spotted during the closing procedures because the Open AP report total will not match the balance in the AP general ledger account.  This type of error will also show up on the audit routines which should be run as part of the daily closing procedure. Once this type of error is discovered you should contact your system administrator or Cove systems personnel for assistance.  They can then determine the cause of the error so it does not re-occur and correct the general ledger so that it properly reflects the invoice activity.

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Invoice and payment are entered using wrong vendor.