No Disk -- \Device\harddisk3\dr3

Googlebait title for a problem I was having with NCover 1.5.8 on my main desktop machine at home over the weekend; whenever trying to run nUnit or FxCop inside NCover, they were raising one or many (respectively) dialog boxes with thie message.

Except if I was invoking this from an MSBuild step inside Visual Studio (either a post-build event or an AfterBuild target.

The internet was not very helpful, but the hints led me to Control Panel > Administrative Tools > Computer Management > Disk Management. There I could see that Disk 3 was one of the slots on the media reader -- the one with the slightly dodgy memory card from my old camera currently in it.

Pull the card, problem sorted.

I still don't know what filing system operation was looking at the drive to cause the error -- and more, why running inside Visual Studio fixed it.