LSU stands for Laser beam Scanning Unit and from what I see in my searches there could be dust on the polygon mirror surfaces, or the motor that spins the polygon may be failing or has failed.
The links below show just a couple of other discussions about this;
If you have already cleaned the mirrors but that doesn't help, it looks like the printer is on its way out.
Printer 5 yrs old, first problem ever, cannot clear this error code? Guide simply states you wipe and clean glass, and surrounding area! no help?