amember not allowing signups for some price groups

Greetings,

I am using version 3.3 and have many different price groups set up for my club membership. currrently only price group -1 works. the other five do not. the registration form shows up and allows to input data but will not submit the information. when people click the continued button nothing happens i have tried to rebuild the database as i thought it was a database error but this did not solve the issue. the website in question is www.lvtriclub.com. I submitted a support ticket and got this answer

I have checked signup form with price group=-2 and there is a javascript error in your custom code
"TypeError: document.SignupMain.elements[FirstNameField] is undefined
var FirstName_Check = document.SignupMain.elements[FirstNameField].value;"

Here is a part of code with above line which raises the error
function CheckFirstName(FirstNameField, FirstNameFieldName, FieldRequired){
var ProcessForm_Check = true;

var FirstName_Check = document.SignupMain.elements[FirstNameField].value;

I not great when it comes to coding javascript. i was hoping someone can point me in the right direction of the file to removed the custom code as the individual that orginally set up our installation is no longer a member of my club.

Thanks
JC

Thanks I updated my ticket with this link as requested. any help would be welcomed.

Cheers,
JC