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.