Sounds a little like the HISS system. Do you have two keys, one with the chip in it and a spare non original that doesn't have the chip in it?
My mate that bought my

from me had a similar issue as that
He somehow used the spare key without the chip I had made up for panniers and pie warmer
Well it wouldn't start just likes you say
Well he got the main key and tried it. Well broom away it went
I think Glen could be on the money
Best of luck Richard