The customer's maps should be found in the \InterMapper Settings\Maps\5.7\Disabled folder.
Go to Server Settings > Enabled Maps, and click the check box in front of each of the map's names to re-enable them.
The latest copies of your maps from prior to the upgrade should be available in the /Library/Application Support/InterMapper Settings/Maps directory under the previous version number in the two folders labeled Enabled and Disabled.
For example, if you upgraded from InterMapper 5.6.8, this would be:
/Library/Application Support/InterMapper Settings/Maps/5.6/Enabled /Library/Application Support/InterMapper Settings/Maps/5.6/Disabled
The maps can either be imported using File > Import > Map from those locations or copied into Maps/5.7/Enabled with the InterMapper daemon stopped. Please backup the current maps before doing this. After the copy, restart the service.
If you have a lot of maps, monitor a lot of devices, or have a large amount of accumulated chart data, or all three, the daemon startup can take a while.