V70: ?Immobiliser erratic?

[bizzylizzy]

Has anyone experienced similar problem. For weeks ignition key starts up brilliantly from first start, warm start, long interval etc. ok.
Then for no reason one day it just refuses to fire or make any attempt to fire. After using fob to lock and unlock doors from inside car sometimes will then start. Other times need to open and close door as well. Somnetimes this works sometimes it just decides to fire up like a good un aftyer about 7 attempts.
I know it will start eventually but when you have just 'nipped in' somewhere and dived back into your car which then refuses to perform you feel daft or worse still worried if the traffic warden is on the horizon !

This problem seems to go on for a few weeks then disappears as suddenly as it came. Have tried using 3 different keys but same problem on all three.

Thanks for any help. Would be really appreciated.