I tend to stay out of the log viewer (unless I'm experiencing a problem with avast that displays an error to the screen) as many of the messages are verbose and of little use to anyone other than one of the developers.
There are many legit reasons why something can't be scanned and the message is more worring that the problem.
If you get virus alerts they are recorded there, so presumably you have already done something about the virus alert when they occurred as they require user input of the action to take ?
All in all I would say you have nothing to worry about.
However, you didn't say what the file names and locations of the virus alerts were, you could physically check if a) they are in the avast virus chest, infected files section (don't go poking around the other sections, you will only frighten your self again, see below) or b) check the original location and see if the file is there, or c) if it's in neither location do a search for the file name.
