I'd like to add something else I discovered while sorting out the same bug. And that's the price. If you're trying to do a test at $0.00 (like E-Junkie suggests you do) and have it go directly to Paypal, you get that error. Paypal can't read 0.00 as a price, even though E-Junkie can. So if you're testing things out, make sure you fix the price to at least $0.01 and then the Paypal buttons will work beautifully.