Onepage checkout problems - no errors but order not placed

[kcaluwae]

I installed and enabled onepage checkout (OPC).

 

When checking out there're no errors. The page itself works fine. Customers fills in all required fields and can click the continue button.

Customer gets the next screen : "your order is being processed"

 

Then he gets back to the OPC screen. Fields are blanked, his products are still in the basket.

 

Order is not placed at this point.

 

 

Workarounds that work :

- disabling OPC

- if the customer creates an account upfront and logs in the order is placed as well.

 

Thanks for some advice.