Hello again grumpierer.
Do you have a version of NMS that was downloaded from Norton servers and activated by supplying an activation code/key? If so then you will probably find that the final few digits of your version number differ slightly from what is relevant to the product supplied by the Android Market. Given the two products are licensed in slightly different ways the software is slightly different and therefore the version numbers are slightly different. If your like mine is 2.5.0.384 (I got mine off the Norton Severs) and the Market version is 2.5.0.390 do not worry. However if the Market version moves to 3.5.0.100 or similar and yours does not move then you have reason to be puzzled.
Does the make sense?
If your current NMS software was obtained from the Market then my first guess would be that it sometimes takes a while for the versions to update around the globe. I noticed that my version of the Android Market itself took days to catch up with what was in use in the USA recently (I am in the UK). Where are you?
