I have: Avast Home 4.7.1074, Windows XP/SP2 w/all updates.
When avast scans D:\Program Files\Microsoft .NET#.dotnetfx.v1.1.exe (the actual MS download file name is dotnetfx.exe; I modify it), I get this result:
D:\Program Files\Microsoft .NET#.dotnetfx.v1.1.exe[Embedded#000ee12]\msi.dll [E] CAB archive is corrupted. (42127)
And when Avast scans D:\CDs\VRMPCCP_EN (Windows XP Pro Upgrade wSP2)\DOTNETFX\DOTNETFX.EXE, which is a file copied straight from the original, legitimate, OS CD, I get this result:
D:\CDs\VRMPCCP_EN (Windows XP Pro Upgrade wSP2)\DOTNETFX\DOTNETFX.EXE[Embedded#000ee12]\msi.dll [E] CAB archive is corrupted. (42127)
Note that [Embedded#000ee12]\msi.dll is appended to both file names.
Files that can’t be scanned are just that, not an indication they are suspicious/infected, just unable to be scanned. By examining 1) the reason given by avast! for not being able to scan the files, 2) the location of the files, you can get an idea of what program they relate to.
Files indicated as being corrupt could be just that the avast unpacker couldn’t be able to handle the archive (or packaging).