i find it odd after looking in the hyster manual for this unit that in the alarm code list it does not show this code.
But after looking through a couple other zapi controller manuals i did find it and do remember dealing with this before on a halloutte star26J after i had to replace the zapi motor controller on it.

What is happening is the firmware information stored in each memory chip in the MDI and the controller do not match or is missing like was mentioned by NERO. The system sees this and triggers an alarm code AL94 while the system updates the information in the component that is at fault. This will occur for 60 seconds and controller is diabled while this is occuring. When it is complete the controller will turn back on after you reset the estop or keyswitch.

Now if you have not replaced a controller or the MDI and it is doing this i guess it could be a faulty connection on the MDI connector but it also could be a bad MDI all together or simply a wire harness issue like a broken wire.
First i would do as NERO suggested and check the molex connector and the wires and connector pins and make sure they are locked in place in the connector.