What does Check is not valid, either assign a different number or clear the existing number to continue mean?
In accordance with best accounting practices, the 2017 first quarter release included an enhancement that prevents duplicate alpha-numeric check numbers within the Assign Check Number process. Previously only duplicate *numeric* check numbers were prevented.
For instance, you can no longer use **ACH** as the reference for multiple transactions. Instead, you could use **ACH** followed by the date with no dashes: **ACH033117**. If you had multiple transactions you may follow them with a letter such as a,b,c... Example: ACH033117a, ACH033117b, etc.