jself: If you have an N800, then you're getting the error because the N800 doesn't have a light sensor. That feature was introduced in the N810. There might be a place in the application to disable checking of the light sensor, if so, disable it.

And yes, battery life estimation is a bit of a black art, and different programs give different estimates.

It reminds me of the old saying: "A man with one watch knows what time it is, a man with two watches is never sure."