When I try to reply to a potential bidder's question I get this error

[bgbay]

You don't have permission to access "http://www.ebay.com/cnt/ReplyToMessages?" on this server.
Reference #18.1adfda17.1629299878.d71baeac

[somanypostcards]

I got a similar message last week.  Here's a possible work around.  Click on Bids, then click on the bidder's eBay user ID, and finally click on Contact in the upper right.