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?
I’m 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 “someone has replied to something” 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.
It’s not even clear what “You are not allowed to create a post in reply to another post” actually means.
Sounds almost like
Post
…Post reply
… …Post reply (no sir you cant)
I’ve 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 it’s OK here!
Sorry, I couldn’t say whether they were or not? I’ll have to see next time it happens
I’ve seen it a few times (includng yesterday), always in areas with comments enabled. See also this.
Same here on that exact post too.
Edit: I think perhaps we’re supposed to “comment” on the reply we want to respond to, rather than creating our own new response?
Apparently this is exactly what happens. If you add a general reply to the topic using the blue “Reply” button at the end everything is fine. You can then even quote as many passages out of other posts as you like.
If you reply directly to the post of another user using the reply button under the post you will get the error messages because Discourse expects you to use the comment function instead.
I had the same error message and when I tried the different options this was the result.
Just had a similar sort of an issue here: Irrelevant locality names - #3 by SimonPoole
Teknoboy added a comment to ask a question.
When I then added a comment to reply to them, it told me that Comments are limited to 600 characters, which isn’t a lot.
I then added a reply Irrelevant locality names - #7 by Fizzie41 but there was no way of actually quoting his comment?
Comments seem to be in general somewhat a 2nd class citizen in Discourse. In any case it would be nice if there was a way to convert comments to regular replies and the other way around.
Oh yes, and this is going to get some knickers in a knot: there doesn’t seem to be a mechanism to report (or moderate in general) comments.
… or even just select text and just click “quote”, actually, or as @dieterdreist found, reply by email.
Correct, by doing so a direct reply to the post is startet, attracting the error message. Havn’t tried the email thing but I’m sure @dieterdreist is correct.
Looks like the only thing you can do is to copy text out of a comment and paste it into the reply window. If you want it to look good, you can even add the quote manually … like in the good old days … 
), for instance
The plugin being used for Q&A is a great candidate for exploring if its development can be “sponsored” by OSMF and prioritize solving some of the issues commented on this topic.
