You have to have chat enabled (tools > options > chat. Tick 'enable chat' & apply). Right click on the column headers in the search results, downloads & uploads windows... tick 'chat'. This will show you peoples' chat status.

If you see a smiley right click & choose 'chat with host'. A chat window will open.

Sometimes it just doesn't work though! And often, a host's not sitting at their computer so your chat might not be seen.

Just seen your other post as well, PMs are not the same as chat. Send your PM regardless of the error message, it will go through. Please don't post related questions in different forum sections... it causes a giant PITA & makes it very hard for people to answer you properly.

**Replies to posts aren't working at the moment.
Reply by PM will work. You'll see an error page but the message still goes through.
Else, start a new thread titled "your original thread - merge".
A moderator will merge threads when they get the chance.