Quick take: 99% of the time, you’re not on a simple pixel layer. Set the Layer 0 baseline and the error vanishes.

Do this first (ActionSeps baseline):

  • One layer only. Flatten or delete extras.

  • Unlock it → “Layer 0.” If it says Background, double-click to convert.

  • Rasterized pixels. No Smart Objects or live effects (Right-click → Rasterize Layer).

  • RGB / 8-bit. Image ▸ Mode ▸ RGB Color + 8 Bits/Channel.

If it still complains:

  • You’re probably on a mask/Channel/Path. Click the layer thumbnail (not the mask) and press ESC to exit Channels.

  • Sanity check: Select ▸ All, then Layer ▸ Duplicate Layer…. If that works, rerun the action.

  • Still messy? Stamp visible (Shift+Cmd/Ctrl+Alt+E), rename it Layer 0, try again.

See also: /fix-command-select-not-available-photoshop, /levels-not-working-photoshop, /need-help-separating-actionseps