Meaning of: COULD NOT CHANGE SESSION, CHANGING SPEED ERROR, ERROR SEED KEY ?

[OVERSPEED]

Can someone explain the meaning of these (an any other error if you can) ?

Or point to some directions (just curiosity)

[morgano]

That "Could not change session" is the error my kessV2 shows when trying to read or write Ford Focus 1.8TDdi Visteon. Protocol FORD J1850 PWM. Still couldn't manage to get answer from "chinese engineers" what is all that about, .

Changing speed error, seems the starting of communication is made at one speed (baudrate) and after passing first negotiation (normally low speed) the link is renegotiated and try to go to high speed for huge data transfer, if this negotiation fails then you get this error. (This is a guess)

Error seed key, this one is easiest, the sw you have is not passing the correct seedkey to the ecu to enter security mode. Reasons... bad coms, missing seedkey, original seedkey in ecu changed by previous tuner... etc.