Checkout returns to payment screen ONCE only

[Sadruddin]

Hi.

I have a number of difficulties.

1: I can't migrate to 2.0.26d, but that's on another thread.
2: As a result I'm using 2.0.24b but Joomla is fully up to date.

I had an IPN error notification from Paypal, now resolved (as far as Paypal are concerned)

HOWEVER when paying (Paypal is my only payment method) a customer repayment returns to the payment screen once.  If they hit the pay button again, it goes through to Paypal.
The problem is, many are just cancelling their payment and trying again.  And again.....

One thing, I do NOT have OPC ticked.

Help?  This is making things really difficult for customers and my admin are tearing their hair out.

S