Was trying to upgrade from 1.7.5 to 1.7.8. Was getting HTTP 500 error messages. Upon further investigation, as another post suggested, I turned on full debug and saw the error stemming from line 126 (as I recall). In any case, I commented out this line and was able to upgrade.
With this line commented out, I am seeing a couple issues saving Schedules and moving displays into groups. When the save button is selected, the wheels turn and turn, If clicked again, another spinning status indicator appears.
The line I have commented out is :
// PDOConnect::configureCache((isset($cacheDrivers) ? $cacheDrivers : null), (isset($cacheNamespace) ? $cacheNamespace : null));
If I re-enable this line, I am back to error state.