Internet Sharing Problem

I've started having a problem sharing my internet connection via airport. As usual, I would go to systems prefs> sharing> internet sharing w/airport checked. After starting, I get the usual arrow in the triangle thingy showing on the finder menu bar, but the arrow goes off after just a few seconds. Below is a segment of my system log. Any thoughts? Thanks, Jim

20" iMac 2.66 GHz Intel Core 2 Duo, 4 GB 800 MHz DDR2 SDRAM, OS 10.5.5

system log ....
Dec 16 11:02:03 James-iMac com.apple.launchd[1] (com.apple.InternetSharing): Unknown key: SHAuthorizationRight
Dec 16 11:02:03 James-iMac kernel[0]: AirPort: Link Up on en1
Dec 16 11:02:03 James-iMac named[395]: starting BIND 9.4.2-P2 -c /etc/com.apple.named.conf.proxy -f
Dec 16 11:02:03 James-iMac named[395]: running
Dec 16 11:02:06 James-iMac kernel[0]: AirPort: Link Down on en1
Dec 16 11:02:08 James-iMac airportd[387]: Error: Apple80211Scan() failed: Resource busy (16)
Dec 16 11:02:08 James-iMac airportd[387]: No networks found on channels remembered for Jeanie's iMac
Dec 16 11:02:08 James-iMac airportd[387]: Could not find "Jeanie's iMac"
Dec 16 11:02:08 James-iMac airportd[387]: Error: Power unexpectedly off, bailing - Apple80211GetPower() = off (0)
Dec 16 11:02:08 James-iMac airportd[387]: Could not find any preferred networks; trying broadcast requests..
Dec 16 11:02:14 James-iMac System Preferences[371]: Error: Apple80211Scan() error -6
Dec 16 11:02:14 James-iMac System Preferences[371]: Error: __performScan() failed (-6)
Dec 16 11:02:18 James-iMac airportd[387]: Error: Apple80211Scan() error -6
Dec 16 11:02:18 James-iMac airportd[387]: Error: __performScan() failed (-6)
Dec 16 11:02:19 James-iMac airportd[387]: Error: Power unexpectedly off, bailing - Apple80211GetPower() = off (0)