panthripu

Hi friends
We have one siemens masterdrive in one of our application.Just three or four months back we wound it is showing over current fault and thisfault is coming before starting the drive. Even if we switch offcontrol voltage and switch on , it shows over current fault immediatelywithout running drive. We replace the drive with spare one and found it running.
Now this newdrive after running for three or four month has got the same problem.We dont have spare drive now.
What is the reason for this kind of problem. I suspect there may be some problem with current measuring circuit but i dont know how to check and solve it.