I'm afraid this is just one of the weird things that eCart does now and again - removing code, causing errors in other areas of code. We had Ray / Jason resolve it for us because there was no rhyme nor reason to it but I couldn't honestly tell you what they did because it was way above our heads. It certainly wasn't anything we were doing wrong though - we were just making changes to the jQuery validation via the wizard and it would subsequently wreck other areas of our page.
Tread with care is all I can say and always make a copy of your page when it WAS working, prior to making any changes. It's not a great way to have to work but it's the only solution sometimes when using WebAssist extensions even if it is just to prove that you're not going mad!