From where are you downloading Adobe Digital Edition(ADE) and which version?
Lets uninstall Adobe Air from your machine and re-install it from http://get.adobe.com/air/?promoid=KEWEJ
Reboot the machine and try downloading ADE 2.0 from the below link.
http://www.adobe.com/in/products/digital-editions/download.html
Once downloaded, install it on you machine and login with you adobe id/password to authorize it.
Check if you are able to read epubs now.
Let me know in case you get any issues while trying the above suggestions.