After running with no problems since I installed it several weeks ago, Private Messaging has basically stopped working. At first I had some functionality when I switched browsers from Firefox to Microsoft Edge. Edge now doesn't work either, and I am being told that Chrome has similar problems. Whenever I try to send a message, I get a white screen with the message:

The requested URL was rejected. If you think this is an error, please contact the webmaster.

Your support ID is: 15718313434588679696

(That support ID changes each time, of course)

One forum member, using Chrome, has reported that he can send short one sentence messages, but when he tries to send longer messages, he gets the same screen as I described above.

Using Safari on my iPhone, private messaging sometimes works and sometimes doesn't.

Although I first noticed it in private messaging, this now seems to have spread to the rest of the forum.

Has anyone else experienced this? Any suggestions about what is causing it. My forum is basically shut down and people are going to just give up if I don't fix it soon.

I don't think it's a Wordpress problem as the rest of the site is working fine.