Unable to comment on posts, error received

Hello,

I’m running the latest version, 2.8.4 and visitors to my site are unable to comment on posts. No matter what theme I’m using, the following error appears when “comment” is clicked on:

Bad Request
Your browser sent a request that this server could not understand.

I searched the forum and did a lot of googling and was unable to find a resolution.

Thanks for your help!