Try Maintenance>Virus Chest>right clicking>restore
If that does not work, is there any way to copy those files again. You might have to delete the contents on the USB drive then replace them.
The three alerts begs the question, wouldn't be safer to keep them in the chest and not transfer the detected files to someone else's machine let alone your own?
Dell Inspiron, Win7x64 SP1, Pentium Dual-Core, 6 GB Ram, Avast Free 2014.9.0.2014 beta, Comodo Firewall 5.12 w/D+, MalwareBytes Premium v2.0 beta, MCShield, Super Anti-Spyware Free, SpywareBlaster, Bitdefender TrafficLight, OpenDNS Premium, Keyscrambler Personal, PrivDog. CCleaner, Greenshot, Firefox (latest build) and, Google Chrome (latest build).
When you do something, do it with a purpose and do it on purpose.