Does the car run on inspection? If it does you need to tach the car and make sure that the speed of the car matches the command velocity. I've seen this fail if the brake is dragging or even if the machine is empty of oil causing excessive resistance to the motor.
Is this an AC or DC job? If you have not already, check the encoder power supply. It may be 12 volts or 5 volts depending on the equipment you have.

when you first log on to the system does it say the floor tables are invalid? where are you getting this 27 error, is it while running on inspection? The 27 error in the motion excuses error log is a performance comparator fault indicating to much difference between the velocity command and the velocity feedback from the position encoder. if the car will not run on inspect from bottom to top without errors the floor table will not be updated. You must set the inspection speed to 30 fpm to run a floor table update. If you have already replaced the encoder, check the brake dragging like Lift-tech advised. also the tachometer is also in play in this closed loop system. you may have a bad tach which is giving you incorrect velocity which the encoder is reporting back to the cpu. I would say first correct the 27 fault, get the car to run on inspect without faults and the do a floor table update. also just so you know the dzu and dzd sensor on the car top must be functioning properly to get a floor table to update, you will notice the car slow down as it approaches a floor on a floor update run, this is so the system can take a snap shot of the absolute encoder holes programmed into each floor. you can check to see if dzu and dzd are working by looking at the appropriate led on the relay i/o board. one last note i have lost floor tables after power outages, and am usually lucky enough to just do a floor update, but a couple of times I have lost many parameters in the cpu and the digital drive. by the way do you have a digital drive, analog drive or an baldor ac drive?

Sounds like an encoder or a tach......check your speed versus demand

Sounds like a bad relay pilot board, if that fails, try MSU board.

I have had this problem a couple of times, both times a 27 error occurred, one was corrected by a new tach, and the other by a new encoder