I got this error while trying to post this the first time. After clicking the button again it gave the same error and asked whether I wanted to reply to https://community.openstreetmap.org/t/how-to-tag-a-railway-track-side-equipment-box-cabinet/103245/3 or https://community.openstreetmap.org/t/seattle-healthy-street-classification/103253 (which I had recently voted up, but was otherwise unrelated).
To successfully reply I had to copy the text, discard the reply, reply again and paste the text.
Weird. Were you navigating that second post while the compose window to reply to the first one was open?
Iām trying to think how to replicate the issue again in case we need to report it.
Thanks
No. I voted the first post up first, then went to the second link (either via an email link, via the āsomeone has replied to somethingā link at top right, or via the list at the bottom of the screen), read that, quoted part of it and replied. The quote is clearly of text in that second thread.
Itās not even clear what āYou are not allowed to create a post in reply to another postā actually means.
Sounds almost like
Post
ā¦Post reply
ā¦ ā¦Post reply (no sir you cant)
Iāve seen this as well. The behaviour seems somewhat inconsistent, when I tried to replicate it a couple of days ago it allowed a reply,
Just had the same thing occur attempting to reply to a thread:
Same thing happened both when I quoted that line, & also just hitting the reply button?
Edit: But trying again by highlighting that line, then pressing reply (which is what I did previously) worked the next time! 
Just had it happen again, after I had quoted a line to reply to. Deleted the quote & just replied & it worked, so that may be the issue?
Were all those issues in Help and support and Tagging help & support (i.e. potentially related to the new Q&A plugin) or do they occur in normal threads as well?
Testing quote
Which worked so itās OK here!
Sorry, I couldnāt say whether they were or not? Iāll have to see next time it happens
