Yes. We have had that problem in the past. What we learned is that those people usually had an existing PayPal account, but wanted to pay as a guest so weren’t logging into their account to make the payment. PayPal’s system recognized them (we were never sure if it was because of their email address or their card number–I suspect it’s email) and didn’t want to allow them to pay outside their account. First have them try using a different email address on the PayPal payment end of things (they can change this on the online form they complete to make a payment) and see if that helps.
If not, they should call their credit card issuer to see why the card can’t be used. We have found that some cards don’t allow payments through PayPal, and on a couple of occasions, for larger purchases like our virtual annual meeting, their cards had a low limit for online purchases.
One thing to note: Calling PayPal about this, IF you can find a phone number, is useless.