Just because you are using PayPal as your payment processor does not mean your ticket buyers need a PayPal account to purchase tickets, they can also use credit cards.
First, login to your PayPal account. Click on Profile and then More Options.
Choose My Selling Tools on the left hand side, and click on Update to the right of Website preferences.
Scroll down to the PayPal Account Optional setting. Make sure that On is selected. That's it, you're finished!