PayPal subscription button not going to paypal page.

I have configured my PayPal settings in my Pro Site plugin and set up Levels etc. When I click on a package level and then the Subscription button for PayPal, instead of taking me to the PayPal page, it redirects me back to my site page where I subscribe?
I was going to open this in the Plugins Live Chat a few moments ago, but some reason is not open and neither is the following session.
I cannot proceed until this is fixed. Help needed.
Regards
Peter