WHMCS runs on PHP code and requires several PHP extensions in order to function normally. If there is a problem with PHP on your server, you will experience problems in many areas of WHMCS. Troubleshoot and resolve 500 Internal Server Error messages in WHMCS. Troubleshoot and resolve Allowed memory size of xxxxx bytes exhausted errors. Troubleshoot and resolve ExceptionLoggingTrait Class Not Found errors. Troubleshoot and resolve InvalidArgumentException: Data missing errors. Troubleshoot and resolve Legacy Smarty Tags errors. Troubleshoot and resolve warnings about the OPcache PHP extension. Troubleshoot and resolve PHP Fatal error: Maximum execution time of 300 seconds exceeded in /path/to/file.php errors in WHMCS. Troubleshoot and resolve Required function is not available errors. Troubleshoot and resolve Segmentation fault errors. Troubleshoot and resolve TypeError: Return value of convertIniSize() must be of the type int errors. Troubleshoot and resolve TypeError guessFileExtension() errors.