50 — fuser error
On a laser printer the fuser is the hot roller that melts toner onto the page, and a 50 code means it isn't reaching or holding the right temperature. Switch the printer off at the button and unplug it for at least half an hour, both because a cold restart occasionally clears it and because the fuser is genuinely hot enough to burn you. If the code returns after that, the fuser needs replacing. It's a consumable part on many business models and a service job on others, so check which yours is before paying for a diagnosis.
Related codes: 50