"Import from Scanner" greyed out in Preview app

Solution 1:

You can try below steps:

1. In System Preference > Printers & Scanners, press Control and click the printer and click Reset Printing System. This will remove all your printers.
2. Go to Utilities and open Disk Utility. Click Macintosh HD in the left panel and then click Repair Disc Permissions in the right panel.
3. Restart your computer.
4. Re-install your printer.

Solution 2:

Turned out my problem was that the scanner wasn't connected. Plugging in the USB helped a lot.

Solution 3:

Before reseting & restarting, I recommend trying just step 2: Go to Utilities and open Disk Utility. Click Macintosh HD in the left panel and then click Repair Disc Permissions in the right panel.

If that isn't sufficient, then go through all the steps that Chunghao gave.