I once had a major credit card problem with PP. What happened is if you register CC numbers more than 5x in 24 hours, it triggers an automatic hold on the entire account; the only way to fix was to physically call them by phone and speak to their security folks. This problem was not fixable through the website and my account was locked until I called them.
The phone PP person was surprisingly a real local American, not a call center in some other country. He explained that fraudsters log on to hacked PP, max out a card, change cards, then continue buying. How they arrived at 5x over 6, 7,8, etc., I don't know. PP related fraud is very widespread, that is why they are so strict.
The reason I had 5 changes is I use a CC service that generates a hash version of a CC number, to be used only once, and for one vendor. Alas, I didn't know this hash number was refused by the PP system, so when I made the purchase it said CC invalid. After 5 tries, I got locked out. Other than that I've been problem free with paypal since they were founded.