Sanguinololu 1.3a X axis stepper motor shaky movement

Hello
I am having problems with the movement of the x axis using a Sanguinololu. The printer was initially working fine but after pausing a print the motion of the x axis has become erratic. The axis shakes from side to side as shown in video below.



All other axis move smoothly. I do not believe the pololu stepper controller or stepper motor is to blame as the motor runs smoothly when connect to another axis and swapping the pololu with another controller did not solve the problem. I have also tried re flashing multiple versions of marlin firmware to the board but this did not solve the issue. Any suggestions to the cause of the problem would be appreciated.

Thanks

Looks like it could be a broken wire on to the stepper. Since you say you swapped it to another axis and it works fine. Check the solder joints on the PCB connector for X axis and under the Pololu Socket for X.