Well you need to access the log via the command line (or file explorer if this is a local machine) and check out /var/log/airtime/zend-php.log
A command you can type in is
tail -n 200 /var/log/airtime/zend-php.log
This will show you the last 200 lines of the log and hopefully will contain whatever error is triggering this problem. If you share the error then we can share some possible solutions and figure out what started to go wrong.