i've had it a few times on low end shit mate, managed to sort it hopefully today, I used copper grease on the axle, and following the befamed 'tester's advice, tightened crank bolt up as much as i dared, just done about 18 miles on it, so Jah willing, all will be good
I've had this happen, once with square taper and once with gxp.
I should probably buy a torque wrench.