Fatal error: Allowed memory size of bytes exhausted when clicked on system>error logs on Admin Panel of Opencart then simply delete the error.txt file from ftp www>system>logs & your problem is solved :)
PS: Keep a check on your log files regularly to avoid further issues
Warning: require_once(../config.php) [function.require-once]: failed to open stream: No such file or directory in<path of website>\wwwroot\library\category-functions.php on line 2
Fatal error: require_once() [function.require]: Failed opening required '../config.php' (include_path='.;C:\PHP-Pear\pear')...