are you sure you have .net 3.5 sp1 installed?
ok, are you sure your completely extracting every file in the zip file to a new folder? not just honorbuddy.exe?
try clearing out your plugin folder and see if that makes a difference.
if you're in EU, use hb 5771
if you're in us, use the new one
it's just a file that's corrupted
Fresh installs of HB 2.0.0.5785 and repaired .net 3.5 sp1 and reinstalled its updates, same error.
are you running hb as admin?