Well, I was using Indigo with ADT v20 and everything was just fine, but I suddenly received an annoying update message to update the sdk.
When I updated the sdk, I got another issue that I need to update the adt due to the current version of the sdk not supporting the old adt. So I did and now clicking on AVD Manager shortcut or going through Windows->AVD Manager is not working. Nothing happens when I click there. Some of my friends are also facing the same problem with Win7 and Ubuntu.
I found a similar question here. But I don't know why that question is closed.