If your A/P Trial Balance matches the G/L Payables Account balance then just quit worrying about this.
As Leslie stated, the system has no requirement to have a record for EVERY possible voucher number.
If you want to do a really final someting you can do this (If you are not technical enough then have your local VAR do this).
This article describes how to rebuild the PM Keys file in Payables Management (PM00400) when you use a Microsoft SQL database.
MORE INFORMATION
Goal: Delete the contents of the PM00400 table and re-create the file.
Kick everyone off the system or do this at night or on the weekend when no other users are on the system.
1. Make a BACKUP of the database that can be restored in case an undesired data loss occurs.
2. Be sure all other users are logged out of Microsoft Dynamics GP.
3. Run the following SQL statement against the appropriate Company database to delete the contents of the PM00400 table:
DELETE PM00400
4. In Microsoft Dynamics GP, click File, point to Maintenance, and then click Check Links to run Check Links on the Payables Transaction Logical File and on the Payables History Logical Files.
a. Change the Series to Purchasing and insert the Payables Transaction Logical File and the Payables History Logical Files. Click OK.
b. Print the File Maintenance Error Log report to the screen rather than to a printer because Check Links will re-create the keys record for every document in Payables Management and will generate a long error log when completed.
Warning: If you cannot successfully re-create your PM Keys, do not continue working in the system because future documents may become corrupted. If your PM Keys do not re-create successfully, you will receive an error message (the message text may vary) and you will not receive an error log.
Mike