If you receive this error in Attaché, check there is no issues with your data. To check the data, do the following:
Make sure all users are logged out of this company.
Restart any computers that had error 1001.
Log in to the same company.
Go to Tools, Data Checks, Database System Status (See: Attache: Run a Database System Status check).
If (as per the article link instructions) all data files come back as a status of Ok, log back into Attaché, open the Maintain Allowance screen again to ensure the error has stopped appearing. If the error persists, please raise a new case online in reference to this article so the Support team can assist.