Issue I stumbled on this weekend when I tried to sign up to a magazine subscription that used the paypal pre-approved payment option it pretty much got me nowhere and I kept seeing billing for $0.00 or getting the error Unable to Bill Order
There is a quick fix for this , and the issue is usually caused by some debit credit cards or what preapproved payment options you have setup in paypal.
visit your paypal account
click on Profile -> My Money -> click on Update next to "My Pre-approved payments"
Click on set available funding sources
now you can select which payment options you prefer to use for pre-approved payments , it best to put a tick next atleast two options. That's it hope that has helped someone who has been frustrated by this issue
note : friends kid had this issue when trying to buy gold on tribes ascend , Unable to Bill Order with paypal approved payments.