Cannot install 5.0.418

After Avast tells me it has successfully Installed Ver 5 on my Vista laptop up comes the message " the application has failed to start because its side-by -side configuration is incorrect
What does this mean ?

Not sure but
What antivirus did you have before installing avast ?
Have you removed it ?
Using ad/remove program, and reboot ?
Have you run the uninstall tool for that program and reboot ? http://uninstallers.blogspot.com/

Have you tried avast repair ?

For a repair of avast. Windows, Add Remove programs, select ‘avast! Anti-Virus,’ click the Change/Remove button from the pop-up window, scroll down to Repair, click next and follow.

I uninstalled Avast 4.8 before trying ver 5
I also used the uninstall tool.

Didnt see any point in Vista Repair as everything works fine (even ver 4.8) before I tried ver5.