Just minutes ago i tried to update my windows xp via ie windows update option.Unfortunately i got a message telling me tht some services (BITS Background intelligent transfer service, Eventlog and Automatic updates) is not running thus windows update is not available unless i start those services.

The interesting thing was all the services mentioned in error message was up & running, so i tried the old & dirty way & restarted windows :)
Believe me if restarting not solves your problem you got a problem.

Then i googled & found an interesting solution & it worked out very well

run "regsvr32.exe wuaueng.dll" command from cmd.

Question was how did wuaueng.dll unregistered?