报错：Down for Maintenance (Err 2) An upgrade is currently in progress… Please come back soon…

参考：https://whmcs.community/topic/219005-down-for-maintenance-err-2/

I had a whmcs the 5.2.10 on the system, i deleted it whole and uploaded the new 5.2.15

I change the version in tblconfiguration:

UPDATE tblconfiguration SET value='5.2.15' WHERE setting='Version';

参考：https://whmcs.community/topic/275149-down-for-maintenance-err-2/
参考：https://docs.whmcs.com/Database_Errors#Down_for_Maintenance_-_An_upgrade_is_currently_in_progress
参考：http://docs.whmcs.com/Upgrading

This error occurs when the version of your database and files do not match. For example if you’re using an older database with the latest files.
Uploading the /install directory which goes with your files version, and running the update process buy visiting the /install/ directory will resolve this.

Seeing this error indicates that the version of the files do not match the version of your database. So for example the files uploaded might be for Version 4.4, but the upgrade script might not have been run yet so the database is still only setup for Version 4.3. To resolve this you need to do a full reupload of the current versions WHMCS files, and run through any upgrade process that is presented to you when doing that and once completed you will be able to access the system again.