Hi, I had a similar problem with a nx100 and hp20 robot, it was without using for about 2 years, encoder batteries were dead, i replaced, zeroed it, and it worked,
but I had the 4328 error and the squeaky noise, I was thinking on lubrication problems, brake release, encoder failure.....
finally a technician reinitialized all the system, clearing all the old data, it was a configuration issue, now it´s working 100%
Hope it can help you.