It's a glitch in the forum software that really, really needs to be fixed.
For some reason, sometimes you have to start a new thread with a simple one word title and then after it posts, you can go back and edit the title to something longer.
Every time someone posts about this forum issue, I just imagine some still suffering addict finds this site for the first time and gathers up the courage to ask for help but their post keeps getting rejected because of this bug that has been going on for a long time now. Not sure why it hasn't been fixed by now.
I'm grateful for the company that owns this forum and keeps it going, but I'd be even more grateful if they'd fix this problem.