Passing Voluum parameters into Aweber form in the background

[Hercules]

Hello,

I have an Aweber form on my website. The traffic source I'm using already has the users first name and last name stored, and so the Voluum link sends these parameters to my lander. I have two hidden fields on my Aweber form that holds these values. I have successfully used the regular, non-Voluum URL to populate these fields https://mydomain.com/?firstname=test&lastname=test2), but when I use the Voluum URL everything breaks and the first name and last name fields are passed as "undefined".

Here is the code that I am using to grab the parameters:

And here is the Aweber form code:

Without Voluum link:

With Voluum link:

Anybody have any idea on how to fix this? It's been giving me a headache for a few hours now.

Much appreciated!