I'm having payment problems as well.

The personal/contact information automatically populated in the first payment tab with no problems; however, I cannot enter credit card information in the second payment tab. In frustration i clicked the paypal button which took me to paypal. I could not complete the transaction as a guest, however ( im not a member nor will I become one). 

So, basically two issues:

1. the credit card information can not be entered

2. Since I started the paypal route, can that be undone?