Portal Sorting help

[James Gill]

I'm not sure if this is the correct place to ask for help with a custom portal sorting function, but I am running into an issue when using portal sort extreme that I cannot figure out.

I've successfully implemented all of the portions of this custom sorting function, but for some reason when it comes time for the Evaluate function to be used on the custom sort_formula field, the evaluate returns a "?".

Looking at the contents of the sort_formula field everything appears correct (contents of field are "." & field_name) and is set up as a global text field but the evaluate still fails.

Can anybody help?