Ok, I think you have not set your paypal correctly in our booking system. Just go to:
Components -> ARTIO Booking
There are tabs and you need to open Payment Methods. Click there on paypal icon and after next page is loaded, click on icon called 'Edit' in upper right corner.
There are 4 important fields.
1. You have probably set published to 'Yes' before.
2. E-mail: here you have to set your paypal email.
3. Currency: As you are using USD for your paypal account, you have to set 'USD' here.
4. Testing have to be set to 'No'.
If you check your settings, is everything right here? Your email address and USD in currency field?