I experienced the same issue, and solved it like this:
1.Install the VC2005 redistributable package which can be downloaded here:http://www.microsoft.com/downloads/details.aspx?FamilyID=EB4EBE2D-33C0-4A47-9DD4-B9A6D7BD44DA&displaylang=en
2. Launch the IRTrans software installer
If you already have connected the IRTrans, the driver will not be correctly assigned to the IRTrans Windows 7 device.
To do this, just follow the troubleshoot options of Windows 7 control panel and it will work.
If you don't know how:
1. Go to control panel / hardware and sound / devices and printers. There you will see a "unknown USB device" or "IRTrans USB device"
2. Right click on it and choose troubleshoot
3. Follow instructions. The wizard will find the appropriate driver installed on the system.