Most likely you have a conflict between the CM driver for Argyll and the driver for the CM display software. You can only use one of them. The other has to be completely removed.
Thanks for your reply.
That would certainly be the case with many devices. I remember I had to switch drivers with the Eye One Display 2.
However the ColorMunki Display is used without a specific driver for both Argyll and HCFR. It appears (in Windows device manager) as a "USB Input Device" under "Human Interface Devices" without any driver installed. I currently have no driver installed for the ColorMunki Display.
In my previous W7 build, I could freely use Argyll or the Xrite software for the ColorMunki Display without switching driver (although I had to stop the Xrite tray before Argyll could access the device).
The xrite software does have its own driver, but I'm having difficulty installing it since I rebuilt Windows 7. The installer loops, apparently loading the driver over and over again until you kill the installer, creating a system restore point each time. It does actually work, provided I let it install the driver at least once before killing the installer, but I don't want to trust software where the installer clearly has a problem. For now, I'll stick to Argyll.