It's sucking too hard - the carpet makes too good a seal with the cleaning head - no air is getting in (not enough air) the motor is racing away off-load (not labouring).
No air = no cooling for the motor - if the machine turns itself off it will be the thermal cut-out safety switch inside.
You should (ideally) be able to adjust the cleaning head to overcome the "gripping" problem.
Good luck...
Peccavi, August 2010
