HPD is standard forklift error code for
"high pedal disable"
In other words, on old tech lift trucks, id you turned on the truck with your foot on the accel PEDAL, the truck would code out to prevent you from engaging fwd or rev with your foot stuck to the floor.
So, you have a twist grip instead of the pedal. It's stuck on, Pot is showing Vehicle manager that throttle is "high". so the truck codes out because you have stuck throttle or "High pedal" and the VM "disabled" the truck.
For Shxxts and giggles, turn the grip slightly one way and restart, then try opposite direction if first one didnt work. It may start up and go. Fix the throttle issue first, and all troubles may dissapear..