 <p>I'm pretty sure you could just go over it to find out why this is happening. You could simply try to debug it, go through everything carefully and make sure everything works. With problems I encounter like that, I like to add excessive things to it, and then slowly whittle it down to where it works. </p> <p>So, to sum it up, in your case, just to make sure, simply try <code>str()</code> to start with, and continue debugging from there.</p>