I'm trying to book train tickets through and keep getting the following error:

E02050 Customer authentication failed, please correct the email address and/or password then try again.

However I'm already logged in, my email and password are both correct and I've filled out all mandatory details on my account. This issue has been happening since yesterday in different browsers. 

I also successfully booked a hotel earlier today so appears this issue is only happening on rail bookings. 

thanks