Well avast 5.0 has been out a year and is very stable from early on, so I honestly can't understand why after a year some people were still on avast 4.8. I'm mean how long does it have to be before you consider something stable.
The 5.1.889 version is for the greatest majority a stable build, but you don't see them breaking down the doors to what is after all a support forum and most who come here because they have a problem, for most it gets solved or a work around found until is gets resolved.
If that person you speak of had done a simple forum search on side-by-side configuration in the forums (or probably just a general google search) he would have seen many such topics about a missing Microsoft C++ installation and when downloaded and installed, end of problem.
-- Side-By-Side Configuration is Incorrect Error - You need to install MS Visual C++ 2008 Redistributable.
You need 2008 SP1 - this is the correct one:
Microsoft Visual C++ 2008 SP1 Redistributable Package (x86)