PayPal error message

I built an e-commerce website which has been working fine until I installed JetPack. I now get an error message at checkout which says “Error Detected, your shopping basket is empty”. The web address at the top of the page is this

“https://www.paypal.com/cgi-bin/webscr?business=gilly%40gillylangton.co.uk&return=http%3A%2F%2Fwww.gillylangton.co.uk%2Fproducts-page%2Ftransaction-results%2F&cancel_return=http%3A%2F%2Fwww.gillylangton.co.uk%2Fproducts-page%2Ftransaction-results%2F&rm=2&currency_code=GBP&lc=GBP&bn=WP+e-Commerce%2F3.8.12.1&no_note=1&charset=utf-8&invoice=&upload=1&cmd=_ext-enter&redirect_cmd=_cart&handling_cart=0.00&tax_cart=0.00”

I called PayPal and they say no information is being sent from my site to PayPal.

If someone can help that would be great.
Many thanks.

https://wordpress.org/plugins/jetpack/