There is definitely an issue with 5.5 and zip code validation. I've now had three customers contact me -- how many are not? -- saying that the site is telling them their zip code is invalid -- while it is not only correct but teh same one they have used for years. If they open a separate billing address block and put the SAME information in, the order goes through. The zip code is not being translated properly -- or at all -- from the shipping field to the billing field