Check the following:

Is the media sensor sensitivity set correctly?
Calibrate the sensor sensitivity.

1. Connect your computer and the printer, and then make sure that the printer is turned on.
2. Start the BPM (Brother Printer Management Tool), click the Printer Function button, and then click the Calibrate button.
3. Check the settings in the Calibrate window.

Is the label size set correctly?
Set the correct label size and gap size.
You can check the settings in the BPM as follows:

1. Connect your computer and the printer, and then make sure that the printer is turned on.
2. Start the BPM, and then click the Printer Configuration button.
3. Check the Paper Width/Paper Height settings in the FBPL tab.

Is the vertical offset setting in the driver correct?
If using the BarTender software, set the vertical offset in the printer driver. To learn how to open the printers folder, see the FAQ: "How to open the Devices and Printers window".