(Eeps... just looked at the Adobe site. They are up to version 4.5 already, and
the 2.01 download link is hidden on the version 3.0 page. I'd keep your own offline copy if I were you. I wonder how long ADE 2.01 and thus forcing downloads of ebooks with old DRM will still be supported.)
It looks as if there may be a problem with your .NET Framework installation. Adobe Digital Editions depends on that to function. CLR20r3 means ADE uses .NET framework 2.0. It's included in Windows 7, as part of .NET 3.5.1.
edit: deleted part of this post. Try this instead:
Microsoft .Net Framework Repair Tool