Tribulant Shopping Cart Problems!!!

Hi.

So i updated shopping cart from an extremly old version and updated wordpress. We are a church and use this as our donations.

For some reason, once someone adds writes in an amount (variable) they get the error “YOU are not allowed to access this part of the site”

If they click it takes them to a blank page.

Has anyone else had this issue? They are unable to make the purchase? is it is the plugin? theme? anyone solved it?

Thanks