Hi Neal,
Some common reasons for PayPal requesting you to use a different credit card are:
1. Credit card is linked or associated with a PayPal account. If you don't want to use another credit card, you can try logging in to your PayPal account, and choose to pay via credit card instead of your PayPal balance.
2. Credit card used to be linked or associated with a PayPal account, or even closed PayPal account. In this case, you will need to use another credit card, or try assigning your credit card to your PayPal account and login to purchase.
3. You have reached PayPal limit on non-member credit card usage. According to PayPal, there is a limit on the number of times, the transaction amounts, the type of merchandise being sold that a credit card can be used within the system without having to verify ownership by opening an account. The restriction is for security and fraud protection reasons. In this case, you will need to use another credit card, perhaps with a different email address, or reister a PayPal account (which is free).
4. Credit card or email address raises flag in the transaction. Try changing either the credit card or email address, or both, when purchasing.
Hope this helps.
Please feel free to email if you have any further questions or issues.