If the 900 error occurs only when the printer is receiving information from a network or computer, contact your software/network support. If the error occurs when the printer is idle or not connected to the network or PC, there may be a printer hardware or connection problem. Sometimes a bad connection with an Internal Network Adapter/Network Card can cause the problem.
The first thing to check is the base printer. If the error does not return, try to print a test page from the Test Menu.
Press Menu > to enter Menus. If the 900 error occurs again before, during, or after the printing of the test page:
S series and K series printers: Continue to press Menu > until you see TESTS MENU.
T series and W series printers: Continue to press Menu > until you see UTILITIES MENU.
Press Select to view the menu items. TESTS/UTILITIES MENU is now on the first line of the display.
Press the Menu > button until Print Menus appears on the second line.
If the display tells you to change paper, press Select or the GO button to print.
If the test page prints correctly, the printer's hardware is most likely working correctly. The source of the problem is probably outside the base printer.
Turn off the printer and remove all options (internal network adapters, optional feeders, second drawer options, finisher options, additional memory, etc.) from the printer.
Then turn on the printer and try to print the test page. If it still posts the 900 error, the printer may need to be serviced.
If the error does not return, then the problem may be with one of the options
IMPORTANT: If you receive an Invalid Engine Code error message when you power the printer back on, there is a problem with the printer. An Invalid Engine Code condition will cause a 900 RIP Software Error message to appear if you try to use the printer. The Invalid Engine Code error means either your printer has lost its stored operating code for the engine board or the printer's engine board has gone out.
Back to Service Error Code List
Source: Lexmark KnowledgeBase