This error indicates that the version of WHASOLS's files does not match the version of your database. For example, you may have uploaded files for WHASOLS 8.6 but, because the upgrade script has not run, the database is still set up for WHASOLS 8.5.

To resolve this, upload the current version's WHASOLS files again and perform the upgrade process. After the upgrade, you will be able to access the system again.

For more information, see Updating and Troubleshooting a Down for Maintenance Error while Updating WHASOLS.