Failure of the "electronic dipstick" is quite common. My last car had this fault but I could get round it by switching the ignition on but waiting until all the ARC lights had gone out before starting the engine (only takes a second). Try this.
If it doesn't work then you can either find another sensor and replace it or bypass it completely. Not sure where it is on the V6 but you're looking for a screw in sensor (brass nut about 20mm across) in the sort of position that you'd expect to find a dipstick. It'll have a plug with two wires coming off it. Unfortunately, unplugging it will just result in the light staying on permanently as it relies on the circuit being complete to put the light out. So you need to run a short wire across both terminals to connect them together.
This will make the light come on with the ignition and go out as normal. OK, you won't have an oil level warning light any more but so what? In reality, these things are about as reliable as a Treasury Forecast and you have more chance of dating Cameron Diaz than getting an accurate indication of the oil level from it. Use the dipstick like everyone else!
Alfa 75 TS LE Veloce
Fiat 125 Abnormale