Error: Check number must be unique occurs when recording a manual check but using the same range as Computer checks.
1. From the Banks page, open the appropriate bank 2. Click Edit account details 3. Select the Payments tab 4. Highlight the Manual Checks row 5. In the Numbering column, select the Start with option from the drop-down list 6. Enter the starting check number in the Next Number column 7. Click Save and Close