The machine has a mechanical problem. Turn off the power switch and then turn it on again.
If the problem continues, call Brother customer service.
If your Brother machine has 2-Sided(Duplex) Scanning feature:
Document might be too long for 2-sided(duplex) scanning. Press Stop/Exit or (Cancel), and use the suitable size of paper for 2-sided(duplex) scanning.
If your machine has FAX function:
We recommend transferring your faxes to another fax machine or to your PC before turning off the power switch.