Some other application with PID xxxxx is also running updates or downloads. only one application can update teh system at any given time. Most likely it is the Update widget that is checking for updates. If it does it all the time you may have a hung process. you can kill that process with the kill command. PID = Process ID
kill PID
where PID is the reported process number.
If you want to see what process it is
ps -A | grep PID
where PID is the reported process number.
Still not working? Can you describe your update procedure in steps from a log on. If there is something simple that can mess something up I am likely familiar with it.