The parser sends the following warning message when trying to use the similar_text function : 

Warning: Call-time pass-by-reference has been deprecated - argument passed by value; If you would like to pass it by reference, modify the declaration of similar_text(). 

The PHP documentation specifies the third argument of the function must be passed by reference, so the declaration of similar_text should be changed by adding an & in front of the 3rd arg to force it to be a reference.

Hope it helps.

Raydjiss