I am not sure why you are getting the windows error sound, but if you wanted to stop it from making this sound you would have to go to windows themes.
In the themes window you'll see shortcuts at the bottom of the screen for windows sounds and it is this window where you can change the alerts, or even remove the sound for this alert by choosing none.
If you are trying to figure out what is happening when you hear this alert, you can download Process Explorer and use this program to see what Processes are running when you hear this alert.
Process Explorer http://technet.microsoft.com/en-us/sysinte...s/bb896653.aspx
Hope this helps.