Just thought i'd let you know that i have sorted the problem. I have just spent about 5 mins on the phone to Ancestry with a very nice Technical support guy who talked me through a couple of things and hey presto i'm now up and running!!
The number to ring (from the UK) is 0800 404 9723 i just told the 1st operator that i was having trouble registering and she put me straight through to them. They are there every week day after 3pm.
Hope it works for you too.
Cathy