@htanabe

I installed again the development version of K2 to your site. The installation completed with a success message however i still see the old layout in the item edit form. This means that probably the new version is not installed properly due to server issues ( incorrect file permissions i guess ) .

Unfortunately you didn't send FTP credentials as Krikor requested so i was not able to verify what i am saying. In any case if this is indeed a server issue you will have to talk with your hosting provider.

Finally after a lot of debugging i found the issue. It's the K2 Multimages plugin. Their code is the one that is executed there, not K2's. So try to update the plugin if there is a newer version. If not disable it or even better, uninstall it.

Thank you for your help.

I thought I replied to this earlier. Just realized my latest reply wasn't posted.

When I first tested by disabling the plugins, I probably skipped the Multiimage, thinking that it was a part of K2.

After updating it, it works fine now.

Again, thank you.

You 're welcome,

Also thank you for sharing the issue and the solution.