Here's link to a description of ProPay. It is a legitimate business.
http://en.wikipedia.org/wiki/ProPay

See the "History" paragraph, which reads, in part:
"Along with PayPal, Skrill, and Paymate, ProPay is one of the select few payment solutions authorized for use on the online auction site eBay."

Perhaps you changed a default payment setting on your ebay account to use ProPay instead of PayPal? You should be able to reset it to PayPal.