Its probably a syntax error.
Easy to solve if its just one file, try using
But what if, as in my case, its a MVC model such as Yii. There are lots of files to check...
If you are using LAMP (Linux and Apache) then run the following from a terminal in the source directory
. -name \*.php -
This will recursively check all php files in the directory and subdirectories for syntax errors.
Full credit to http://www.electrictoolbox.com/php-command-line-syntax-checking/