WSUS MMC is working, Synchronization is working, but WSUS fails to download updates and Self Update is not working

I have WSUS 3.0 SP1 under Server 2008 Enterprise WSUS MMC works fine but i don't know for what reason self update and updates from Microsoft are not getting downloaded. I have checked out the even log and i have come across errors like "Self-update is not working" and "The server is failing to download some updates". Client computers are getting Synchronized properly, problem is just with downloading part. Can anyone help me out ???

Are you getting below error in event log ??
Event ID: 10032 (The server is failing to download some updates.
If yes then you can go through below thread and try out the solution that has been mentioned there. If you don't get any help then you can try using WSUS server debug tool for finding out the exact cause of issue in your case.