On some models, there is a switch mounted in the pallet grab area that is mounted to the platform. You will have to remove the 2 allen bolts and drop down the pallet grab assembly to get access. However, when you do that, it relieves the cable tension so you can't test the actuation process of the switch. Just test the switch to make sure it works with a VOM and if it don't, replace it. Then hold the assembly back up with your hands and have someone actuate the pallet grab to listen to the switch actuate. If you want to definitely see if this is it, bypass the switch temporarily to see if it fixes your problem. Be careful, because I can't remember if it is a NO or a NC switch that is held open. Check to see which contacts have wires on them and check to see how it is actuated, then make the appropriate bypass either with a jumper cable or just disconnecting the switch. Chances are, this is the problem if you have a message that says "No Pallet."

well the fact that it does it when your 5ft off the floor and i'm assuming it does it consistantly in the same spot every time means you have a break in one of the wires in the mast cable most likely.
The only way to check that and verify it is to get a vom meter and check resistance/continuity on each wire and see which one is broken. High resistance or open circuit means a break in the wire generally.
Now if your lucky and the engineers thought enough in advance to add an extra unused wire like i've seen in some harnesses you can make use of that and repair it by moving that circuit to that wire.
But yes... you will need a technitian to do it if you are not familiar with that kind of work.
And furthermore... being a pallet grab problem, that is a safety issue and is imperative that it be repaired.

Sounds complicated, any other reasons? Anything I can check on my own without a technician?

my first thought would be an open circuit in the mast cable

you'll need to get a VOM and check the wires in the cable