Resmed Aircurve 10 not logging correct hours..

Hi,
I know a guy who has a Resmed AirCurve 10. He says the machine is saying he used it for 2 hours
in one night. He swears he is using it for around 6 hours. The date and time are correct on the
machine.

Any ideas what is happening with this?

Depends - if he looked for results after noon hour, e.g. 2 hrs later, all he'll see are 2 hrs of activity because the machine works from noon to noon, so he'd have to look prior to noon for last night's records.