Paypal Not Working Prestashop Version 1.6.1.2

[fizzer]

When anyone tries to checkout via paypal they keep getting the error message:

 

403 - Permission Denied

 

You do not have permission to retrieve the URL or link you requested,   

Please inform the administrator of the referring page, 

http://www.myshop.co.uk/order

 

if you think this was a mistake.

 

I have checked everything I can think of, my folder permissions are 755 and the files are 644. I have checked my paypal api details which are correct, I am in live mode, I have tried with paypal standard and paypal express checkout, nothing works. The checkout seems to go to express checkout regardless of whether I have enabled it or not

 

I need help please as I have no other payment option, so I have had to close my site until it's fixed