Failed to fetch URL https://dl-ssl.google.com/android/repository/addons_list.xml, reason: File not found

I now spent two hours on this issue
* I have no proxy in my system
* I forced 'http' insteas of 'https'
* I deactivated my virus scanner
* I even deactivated Windows firewall
Nothing helped!
Then I had an idea, I am using Windows 7. So if you are using Windows 7 and you have installed android-sdk under 'C:\Programs' then you have to run the sdk as 
administrator!
Windows Start --> Programs --> android --> android-sdk --> right mouse click --> run as administrator.
This helped, now I am able to install new packages. 

http://code.google.com/p/android/issues/detail?id=21359