AutoCAD double click block editor not working

Double-clicking an object, such as text or block, does not open the object specific editor dialog or window in AutoCAD.

Over the past few days, I have been working in AutoCAD on a large layout, normally when double click on a block object, the block editor will open and allow us to make change to the selected block, but I could not double-click to edit the selected block this time, what happened?

Somehow my PICKFIRST variable changed. The PICKFIRST variable allows you to select objects, then start a command and apply to those objects. If PICKFIRST is off (set to 0), you have to start the command first then pick the object. Setting PICKFIRST to 1 or enabling it gets you back to the behavior where you can select the object then launch the command (double-click). Below is a snapshot from AutoCAD help.

image source: Autodesk

How do we change this? You can simply type PICKFIRST at the command prompt and change the value to [1] as shown in the below image.

You can also bring up the options dialog box by type [options] at the command prompt, and navigate to the section modes section and check the Noun/verb selection as shown in the below image.

Now when you double click on a block object, AutoCAD will be able to open the block editor and allow you to edit the selected block as shown in the below image.