If you are using an IRTrans USB module, you need a "driver" to make the OS recognize the module. Please download this package: "IRTransUSB.dmg" (227 KB)
After downloading and double-clicking the package, go on with the installation:

Please refrain from looking for newer drivers on the Internet, because only the provided driver is tested for use with iRed2.
If your system is running in 64-bit mode, you may need to install a different version 2.2.14 of the driver, available from FTDI's website.
Please see the Troubleshooting page, if you encounter problems.