Internal Server Errors are generally caused by incorrect File or Folder permission problems. Note that the files should be with 644 permissions (RW on User, R on group and internet) and folders must be with 755 (RWE on User and RE on group and internet). In all cases you should be able to find the exact error cause when you go to the CPanel->ErrorLog. Note that the latest errors are on top.
If you don’t know what to do to fix it, please open support request from our client’s area and a technician will help you fix it.