ipl file hangs during cgi-callout but not from direct call

System

I have an interesting one. I have an ipl file that I am using for a cgi-callout. It works great when I call it directly from the browser, but when I call it from a DCR in a callout it hangs.

I believe the reason it is hanging is because of the very large amount of data that I am placing into the listbox.

It's strange that it works great with the large amount of data from a direct call to the ipl file from the browser, but not when called via a cgi-callout. If I reduce the amount of option values in the select field down to 20 or so, then it works.

I have attached the code.

This is a side by side listbox that allows the user to move value from one listbox to another.