[Solved] OKI MC362 Printer Problem: Error 990 Troubleshooting - Causes & Solutions for 2-Year-Old Unit

Hello.
I have a problem with the OKI MC362 printer. After turning on the printer, Error 990 pops up and there is nothing I can do more.
I bought a second - new, same printer (I needed another one anyway, and didn't have time to repair it at the time), repositioned the entire toner cartridge and no changes. I also moved the waste toner container and some replacement element that is behind the toner cartridge and nothing helped. I transferred all these parts to a new printer and the new printer works without any problems, so you can rather rule out failure of these components. What could be causing this error? I would like to add that the printer is about two years old and printed about 15,000 pages, so it's not terribly worn out. The toners were replaced several times with ready replacements.

According to https://printcopy.info/?l=en&mod=erc&brand=OKI&model=MC362&code=990, this is a black toner problem.

I bought a second printer of the same type, transferred whatever I could from the broken printer to the new one and everything worked, and when I put it from the new one to the broken one, the problem was the same all the time. I took out some old black toners from the cabinet and in one case the error disappeared and the printer works.