On the Sell Your Item form the 'Paypal details' requested is just the email you use for that account.
Since you have been using eBay for a while, I wonder if you are spelling the address correctly? (Always look for the dumbest possible mistake first, eh?)
It is also possible that they want you to upgrade to a Business Account instead of the Personal account you have now, but usually that is when you start getting paid more often. Fees on personal accounts are lower.
