It looks like there is a problem with our latest installer, compounded by a quirk of windows "uninstall" function that masked this problem on my test machines.
If this is the first time you have installed our plug-in, then follow these steps to install the VCP driver. If you are updating from an older version of our plug-in you DO NOT need to and SHOULD NOT do the following as the VCP driver is already installed (even if you un-installed the older version of out plug-in).
Please go here:http://www.pmdx.com/Downloads_Utilities/
and manually download the ST Virtual COM port driver:
For 32-bit windows: VCP_V1.3.1_Setup.exe
For 64-bit Windows: VCP_V1.3.1_Setup_x64.exe
Save the installer somewhere convenient on your computer and then run it (double-click on the file name). This should install the driver for the PMDX-422. Note that it will actually go through TWO sets of installation dialogs (though you only need to tell it to start one).
If you run the VCP installer and see a message asking if you want to "Modify, Repair or Remove", then click on CANCEL - the VCP driver is already installed and you do not need to install it again.
As an aside, on some Win7 systems, the first time you plug our device in (with valid drivers :-) Windows will try to search for updated drivers (without asking first - how rude). If you see this dialog, click on "cancel".
Let us know if this doesn't solve your problem.