It is recommended to disable maintenance during OpenX installation upgrading
There are two types of OpenX maintenance:
1) Scheduled Maintenance
2) Automatic Maintenance
How to disable OpenX Scheduled Maintenance
In order to disable OpenX Scheduled Maintenance you should make changes in your cron job in order to prevent its triggering. On most systems it's enough to comment the line out with # at the beggining of the line.
How to disable OpenX Automatic Maintenance
In OpenX 2.4 and above versions /openx/var/xxx.com.conf.php file should be changed and set "autoMaintenance" from 1 to 0.