A 449 error is a drive fault error. The control can't /won't even try to reset if it gets a fault input. By forcing the relay, you remove the Z axis brake without the having the control hold the motor so the head falls.
If you have DC drives, look for an LED on the card. On a GA370 Glentek drive card, the light only stays on for a short time so you have to have the door open, watch the cards, have somebody else press the reset button.
After you determine which drive faults, note which LED lights and report back.