What brand and model of CD-RW is it?
Just as a preventative measure, you may want to scan your PC for Viruses, Trojans, and scumware.
For malware use AD-aware
http://www.lavasoftusa.com/
or Spybot
http://patrick.kolla.de/spybotsd.html
For Trojans use The Cleaner
http://www.moosoft.com/
How do you have it jumpered and what is it sharing the cable with? You could also try moving the drive to another channel
and playing around with Master/Slave/CS jumpers.
Try uninstalling and reinstalling your software.
However, a problem that happens once every two months is very hard to troubleshoot and you might be better living with it rather than tearing your system apart trying to solve it.
There also was a joke program obtainable on the Net at PC Jokes and Pranks Websites, that caused similar behaviour; however, I think it would be happening all the time, if that program were installed.