This is a simple and common problem with many LED print head printers. You just have toner dust on the surface of the print head. Run your finger along the head and all will be well.
There is a sensor on the front left side usualy that detects the cover open or closed state. Check it maybe you made a mistake at assembling it or something came in between and the sensor can't detect it.
That is a paper jam code. Reopen the cover, and clear all paper jams. Close the cover, and then I would reset the machine by turning it off and on if the code continues. http://www.german-parts.de/oki_manual/paperjam/stau_b400_series.pdf