Using NCover with the //iis switch

Hi, I'd like to use NCover to analyze a a couple of different IIS-hosted processes (a website and a web service), and I'd like to do this from NAnt. When I run the equivalent of "start ncover.console //iis //x some-filename.xml", if the unit tests don't hit the IIS apps quickly enough, NCover terminates. If I hit IIS in time, NCover says it is connecting, and is presumably doing some work, but never terminates and never writes the output XML file.

What exactly is the usage model with the //iis switch? How and when does NCover terminate normally in this case?