Can you drag & drop whilst all of your plugins are deactivated?
If so its probably a plugin conflict & you can turn them on one by one to test to identify which is causing the problem.
I have tried to deactivated all of plugin, but still no change, i could not drag and drop a widget.
Files might be cached from the previous version. Is it any different in a different browser and/or after clearing your browser cache?
I have tried also on computer and different browser. Besides, I also tried to replace wp-admin, unfortunately that was not change to be good.
Hi Guys,
Finally, i have solved this problem. I have downgrade to my previous backup, and restored it to the server. I have guessed, it’s true that there is problem regarding with plugins. Here it is: BlueProof Security. It change my .htaccess, so i could not update my updateable wordpress, plugins, themes, etc and caused my widget could not be dragged and dropped.
Thanks all.
