Quote by Robin: OK here we go again.
First of all I read all your posts very carefully.

So we eventually got to the bottom of the problem.
When anybody will experience the issue with comments that's the issue described below.
To summarize, the issue is with the additional line of code that is added to the lib-common.php after installing TinyMCE editor.

Comments by and large work the only thing that doesn't work is the Reply button and this applies to all layouts with TinyMCE editor installed plus the additional line in lib-common.php.

And last but not least, sorry to say but this thread is the good example of How-NOT-to report a problem.
You should state in the very first post that you installed TinyMCE, etc. But I guess by the time you found out there was a problem with comments you forgot about TinyMCE.
Thanks to our discussion here I've just found that there are problems with comments on my site now

Quote by heretic:
Try changing the line to