Sorry it's taken a while to get back to you.This can be due to a number of factors, basically any 'major edits' you may have made to the form such as 'adding a background'.Try 'save a copy' and then enable.Bill (who is not an expert)
If only the above suggestion worked!I'm using LC Designer 8 with Acrobat 8 Pro and I've done the above, enabled user rights in Pro and emailed - still sent as XML formatBill