Seems your plate is not in the right position into the drum, this maybe due to caps problem or encoder damaged.
- shut down the machine and check if there's a plate in the drum and where is it
- remove the plate
- shut down the computer with Galielo Consolle
- restart all
now you got 2 options:
1- if it happens again clean caps and rollers (I had the same issue with GTO plates -37x45cm- and I solved by cleaning accurately)
2- if the problem persist after the reboot, sorry, but call for a technician and check together the carriage movement and it's encoder.
Good luck!
G: