It may happen that you are in the middle of a check run and the system locks up. Upon getting the system going again, the check run and bank account may be locked, preventing you from continuing running checks.
To fix this issue, follow this procedure for unlocking a check run / bank account:
1) Go to Administration > Setup > Banking > House Banks
2) The “Lock Checks Printing” check box will be checked if the bank account is locked
3) Un-check the check box
4) Click “Update”