I switched out Access 2 and this worked just fine.
Machine starts.

Checked hydraulic motor, it has good phase to chassie resistance values.

So just a faulty Hydraulic module i guess, machine has been running since 2013.

Will check grounding strap as well!

Correct 722 is a CAN communication error. First make sure the access 2 is getting voltage. The flash code from the access 7 looks to be code 740. It almost sounds like a bad hydraulic motor. I would test that motor. I have also seen this happen when there is a bad distribution board.

Thank you for you reply!

All connections at distributioncard is tight.

When measuring CAN i took one connection off at a time when measuring and then connectivity test between all Access CAN-pins.
Resistances at Display and Access 3 ok.
Controlled cable loom between modules.
Found nothing to complain about I would say.

Today I rented a computer with correct firmware for Crown and flashed the forklift with new vehicle codes just to test if I would get connection with all accesses, this was no problem.

After rekey I now get Error code 722

This code points out an issue with communication between Access 7 and Access 2 if im not mistaken?
Both of these Accesses have power at startup and no faulty CAN-wiring.

Should I replace Access 2 or is this code showing just because of the update of firmware?

I would start by checking all the connections at CA205 on the distribution panel. Otherwise typically it's an access 3 issue or weirdly enough sometimes if the grounding strap is too short this can happen.
When testing CAN did you disconnect any modules? It's best to take readings from 2 or more modules.
My only other thought would be to test the battery under load as sometimes a dying battery can cause this issue.