I just changed the code by removing the .travelclubsworld from the web address (the subdomain bit of it) so now it reads
[s2Member-PayPal-Button level="1" ccaps="" desc="Bronze Member / description and pricing details here." ps="paypal" lc="" cc="GBP" dg="0" ns="1" custom="transporttravelclub.com" ta="0" tp="0" tt="D" ra="0.01" rp="1" rt="Y" rr="1" rrt="" rra="1" image="default" output="button" /]
After making that change and moving through the payment I got to a screen that looked the same, but instead of the error said...
"Thank you! Your account has been approved.
The next step is to Register a Username for immediate access."
Then a button that says "Please Register Now (Click Here)"
After clicking that I went through to the login page though, not the registration page.