Thank you so much for the reply.
You were right - I was using the developer login email address. I set everything up with the main sandbox login address and the payment seems to be going through OK - I get a return to my site with message -
"Your registration process is not yet complete! Please check again your email for further instructions that have just been resent. If you don't find the email, check your spam-box. Make sure that your email account options are not set to immediately delete spam. If that was the case, just try logging in again to receive a new instructions email."
However I don't seem to be completing the registration - the new user is listed in CB User Manager but marked as Enabled=Blocked and Confirmed=unconfirmed - and he can not log in.
The CB log file seems to have 5 entries:-
1. Subscription created
2. Payment basket created
3. Payment record created
4. Subscription activated
5. Payment record updated (time completed updated)
so I think this looks OK.
PayPal history is saying "Payment Status: Complete" and "OK to Ship" so it too seems happy.
Not sure what to check next?
Thanks for the excellent help so far - much appreciated.
arcamna6