I have a store based in the UK on 1.3.8 using paypal payments pro (payflow UK) and paypal express.

I am losing customers due to problems with the paypal express and despite various attempts to fix or find the solution this is still losing me customers on a daily basis.

I have just tested it myself and found that the same error occurs whether I fill my shopping cart then press go to checkout followed by paypal express OR if I just select paypal express straight from the shopping cart

Everything goes smoothly until I press confirm order. I then get this message

ALERT: PayPal Express Checkout Error () -12

and start to go around in circles before eventually giving up!

Does anyone know the solution? It is driving me mad.
Thanks