Crash, exit or high CPU usage when viewing certain directories has suggestions for tracking down the component triggering the crash and disabling it. Qsync probably installs a shell extension, so disabling that is a good thing to try first, as it's the most likely component to be involved.
There should also be some crash dumps which can be zipped & emailed to leo@gpsoft.com.au for us to investigate whether the crash is likely due to a bug in Opus or a 3rd party component.