I have been working with @AARPMichaelP on this problem and have finally got it narrowed down as to the problem.. He has the "experts" working on it but until there is a conclusion, here is when it happens and what you can do about it.
The HTML error occurs on this forum when there is SOME different HTML coding appearing in a post that has been put there by you in a
whether in a copy paste with an embedded link or some other type of type, color, boldness, italic - anything that has HTML code attached to it that is different than the HTML that you are using for your reply..
It can also occur when you might be replying to someone which is using their own special font, boldness, color in their typing here - it occurs when you use the " (quote function key) or copy/paste and they are using some special font/color/size/boldness - that is different than what you are using or the default.
It happens when you are "REPLYING" not so much with an initial post that starts a thread when you are "POSTING" -
I know that @Panjandrum said he/she had problems posting links and I noticed that their normal type size is larger than the default. So what he/she should try when trying to post a link is to change the link to the same size, color, boldness, whatever that they are using for their standard typing.
Same thing for @Roxanna35 with her big red or black type if she want to post a link in a reply. Or wants to use the quote function or copy/paste that is different than her own selection of HTML - I didn't check this thoroughly since I use the default now because of this problem.
I think @Richva has already figured it out cause I notice his/her links are of the same font, color, size, boldness as the type they are using.
To make a "REPLY" take without the HTML error message, you have to actually edit the copy / paste edition that you are posting to remove other HTML - I do it off the board if it is a lot or hard to correct and then copy paste it onto my reply and then post. Sometimes it is sneaky and you have to be aware of what is different HTML.
I hope this helps the ones that are having problems - but a fix does need to be added, if it can, and hopefully will - at 1st, @AARPMichaelP told me the programmers said it was a security issue but then when I told them that I could post it once I edited it to the same HTML that I was using and it took fine - 😯 Their rationale didn't make sense.
When I have experienced the issue, I check the HTML by using the menu option at top of the Reply textarea. It is almost always because of an attribute not recognized by the forum, most notably the <span> </span> tags, which can occur when copying from an outside source, so I eliminate/delete those tags. Also best to "Paste as plain text" to avoid HTML tags not recognized by the AARP forum which uses a more simplistic HTML than later HTML versions. Although, yes, doing that is a PITA when it used to autocorrect.
I am unsure why links posted in different font or size would trigger an HTML error. For example:
Maybe a screen shot using Snip & Sketch of the HTML before posting would help especially if you are having the problem often when you post. If you don't have a problem with the post, then you can delete the imaged you saved.