Epson AcuLaser C4000 Owner's Manual page 310

3. Remove the stack of paper from the cassette, tap it on a flat
surface to even the edges, then reinsert it into the paper
cassette. Be sure the paper is evenly aligned and the top of the
stack is below the metal retaining clip and the maximum
paper mark.
4. Reinsert the paper cassette into the printer.
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Troubleshooting