I've been using PayPal for a while now and never had problems with it. Just recently, I wanted to buy a book on sale for like 3 CHF-ish, and it asked me to add a credit card. I checked my funds, there's enough money to pay for it, however when I tried again, it still didn't work.
I did link my Bank account to PayPal, so why do they ask for a cc now? Not owning a cc is why I use PayPal in the first place.
PayPal allows limited purchases without a credit card linked. Eventually you will be required to link a credit card; it seems that your are at that point now. So, you will need to link a credit now if you want to continue to make purchases with your PayPal account.
