If you see an error like the following:

MSB6006: "NCover.Console.exe" exited with code 1. in build.proj(93, 3)

be sure to check that you are using the correct version of CoverLib.dll. In older versions of NCover (e.g. 1.5.8), by default, this dll should be registered every time the NCover task is run. I haven't found that to be true, though. I had an older version of NCover installed somewhere else on the build machine, and I kept on having my build fail because version 1.5.8 of NCover.Console.exe was loading version 1.5.5 of CoverLib.dll.

By manually registering the correct version of CoverLib.dll, I got the build working again.