There you have a problem having a Navman. The software is not supported anymore neither are the maps. I suppose the maps and software are original?
In fact, the iCN510 is a +10 year old model and is nothing more than a rebranded Mio 136 (Pocket Pc) running windows ce (4.20, in those days, I think). Navman installed their GPS software and locked the system so changes are ... not impossible. The user octosys recently unlocked one. Maybe send him a pm??
I know that in the past, there used to be a website about unlocking all Navman devices (
[Please Register or Login to download file] ), however it has expired and the unlocks have gone. Nevertheless, octosys succeeded.
What should be possible to find on the Internet is miopocket (google) and that one should work, even when it is a very heavy program that weights a lot on the devices memory, so it may not be the best unlocking choice after all.
I think Fatboyfun can help out too. Then there is "danibor lanik" who might have an unlock that works.
Then after unlocking, an IGO8 is ideal to put on it. In any case, don't expect too much. IF/WHEN you succeed, you will be pleased and may have years of fun wit the device and IGO8. But when the unlocking goes wrong, ...