If you maximise the scan report and then move the column headers, all (or most) of the text should be visible.
The sample listed looks to me like a reference to a system restore setting or file.
Whether the files concerned represent a problem or not depends on the full names/paths.
Other security programs (Spybot, Adaware for example) password protect their quarantine areas. Quarantines files aren't a threat.
System restore can harbour nasties. I don't think there is a way of telling what the particular file is without a lot of knowledge and a hex editor. Far easier to just ignore it, as it isn't a threat unless that particular restore point is run. To eliminate it just turn system restore off, reboot, turn it back on. Pfft. All past restore points (and any malware) gone. (Only do this if the 'pooter is in good health, of course.)
This is a pretty common question in the Avast forum. I guess ninety percent or more of the time "unable to scan..." does not represent a problem.