In GE EV100 controllers, codes above about 89 are specific to the truck management interface. Usually (and in this case) 99 is the "maintenance alert".
This just means that someone with a handset needs to reset the hour meter reading when the next service should happen (and someone should do the service correctly).
However it should NOT effect lifting, and should only slow down the traction drive. how good is the battery state of charge? you may not be seeing that you have no battery charge and the lift is going into lift cutout as it needs to be charged or you may have some other problem if this lift is stopping lifting.
BTW, whoever sets the maintenance. alert, can also set it so it never comes on, or comes back when ever it reaches the predetermined hour limit.