If you are seeing Error 81, the Smart Extruder+/Smart Extruder has detected a filament jam.
Sometimes a filament jam is detected incorrectly. To find out whether you really have a jam use the control panel dial to go to Filament > Load Filament.
If no plastic comes out of the nozzle, something is preventing the Smart Extruder+/Smart Extruder from extruding. You might have a blockage. Try unloading and reloading filament to clear it.
Okay, it sounds like you need more help. Please open a case with MakerBot Support. Make sure to include your extruder serial number and shipping information.