On the site that i'm working on, when going to check out, the New Customer account form is no longer working. when entering in all the required form data and pressing submit, the user is presented with a list of validation errors, stating the fields were not filled out, when in fact they were.

we've installed several plugins at this point so I don't even know where to begin.
UPSXML Dimension, FEC etc.

does this sounds like a familiar or typical problem to anyone?

can someone recommend where i might start to track down the problem?