The question is what it is and not how to fix it. While interesting I can answer what it is.
IrDA is a standard which I won't duplicate here but offer a link for reading. Read "Infrared starting Point" at http://rfdesign.com/mag/radio_infrared_communications_using/index.html
At this point you'll have the basic of IrDA signaling.
Next you need to know that IrDA has a standard to replace Serial Cables called a serial profile. You'll see this in Bluetooth as well. The most common usage was to sync PDAs over IrDA.
The IrDA Protocol itself is about the size of a small book so if you really want to know exactly each bit of the protocol is, it won't fit in this response but you can type IrDA Protocol into google.com and get more links.
Hope this answers your question.
Can someone explain to me exactly what a" Serial Cable using IrDA Protocol" is? Device manager says it is not working properly. Is this something I might need for some reason or is it unimportant as far as a missing driver is concerned. Is it safe to uninstall or should I try to fix it? Another words, what is this driver for? Thanks for any help. Windows XP compaq presario SR1820NX.