Commonly that means you may need to switch to an older php version, if your script is using mysql_connect for instance it would need to be set at php version 5.6, don't forget to check the functions you expect to be needed.
There is also an error file accessible under "System Info & Files"-> "Site Summary / Statistics / Logs"
By looking in the Error Log you can get a clue on what may need to be sorted out.