While browsing this thread, I searched for "No Image Handler information found" and saw someone fixed the problem (error message "No Image Handler information found") by clicking on "install Image Handler" on admin page.

I don't know what happened. I did install IH2 and was surprised that there was an option "install image handler" under admin page.

After "re"-install IH2, everything works now!

PS. I have to say that IH is really useful. Thank you very much.