I have had several occasions that a “Head not found” error occurred after powering on my Glowforge.
I realized this only occurred when there was something to be engraved or cut on the crumb tray and removing the item and recycling the power solved the problem.
However when using the rotary attachment developed by taylor.a.jenkins it is necessary to connect the attachment to the gantry with the power off. But then when power is applied, the “head not found” error occurs.
I found that covering the attachment with a piece of black cloth before powering the GF on solved the problem.