Photoshop is confused and can't find the Scratch disk. You may have removed it or changed its name.

Do one of the following:

Press and hold Ctrl+Alt+CShift (Windows) or Cmd+Option+Shift (Mac OS) when launching Photoshop. You will be prompted to delete the current settings.

In Mac OS, open the Preferences folder in the Library folder, and drag the Adobe Photoshop Settings folder to the Trash.

New Preferences files will be created the next time you start Photoshop.