I was wondering why avast isn’t scanning these files?
Decompression bomb is just something that unpacks to an unusually big amount of data even though it’s rather small (i.e. has a high compression ratio, for example). It’s nothing to worry about, you are just informed that avast! will not try to unpack the archive (you may not even know that it’s an archive, but it seems like it is) because it may take VERY long to process.
(quoted from Igor: http://forum.avast.com/index.php?topic=15389.msg131213#msg131213)
I’d suggest to ignore these files.
But you can change values into avast4.ini file to configure how avast should work with these files.
Click ‘Settings’ in my signature for more info 
About the others, than can’t be opened, maybe files are in use at that moment, maybe just a packaging problem… I won’t even worry about them. Archive files are inert by their nature, when and if extracted, the files, if infected, will be detected and blocked.
Welcome to avast forums.
Thanks
You’re welcome. Feel free to come back any time you need help or just to change experiences 8)