This is an error that is not recognized by the Ultimaker 3. Something went wrong, but the Ultimaker 3 cannot provide a more accurate error.
These are quite rare, but can usually be resolved easily.
|Reboot printer||Turn off the Ultimaker 3 using the power switch at the back. Wait a few seconds before powering it on again.|
Update the firmware to the latest version. Older firmware may contain bugs that have been resolved in later versions. Learn more here: