luceos
it's an apache error. You need to check the error logs from apache.
Yes, but my hosting provider doesn't give me any control over what Apache logs. A typical 500-error line from the log is in the previous post:
84.92.117.0 - - [02/Oct/2021:22:33:14 +0200] "GET /u/admin HTTP/1.1" 500 645 forum.oxfordparkinsons.org.uk "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/94.0.4606.61 Safari/537.36" "-"
and I can't tell you any more than that.
You might also want to redirect http to https.
I do this on the main site, of course. I'll add it to the forum .htaccess at some point. But for now I'm always visiting https://...