My Samsung Clp-315 color laser printer showed me a red online led.  Because this means general error you need to connect it to the pc to see what the problem is in the Samsung Smart Panel.  My printer is normally connected to a printer server so the it’s not right away clear what the error was.

Smart Panel told me that there was “Toner waste bin full or not present” error, strange because there was a bin and it wasn’t full.
In the past the printer was transported without the cap on the waste bin, during that moment there was some toner spilled in the printer.

This toner was now blocking the light sensor and therefore the printer was thinking that the bin was full.
After cleaning it all was working fine again.

I think this same solution can work for other Samsung printers from the CLP-3xx series, give it a try.