Aborting installation is the cause, maybe.
As I said before I didn’t have trial license (forgot to get it) so aborted installation when setup prompted to insert license.
However, installation itself seemed already completed and there is an icon in the status bar.

[quote="NON post:10, topic:657860"] - Could not uninstall because of this error: "`C:\Program Files\AVAST Software\Back up\Data\state.dat` is under exclusive use." or like that. [/quote] Was a backup running at that time? My uninstallation worked flawlessly...
No, backup is not started.