Hey nine,
Actually 3.5 isn't qualified to work on 64 bit windows because of the watchdog process. The simplest thing to do if you really would like to use qube 3.5, is to disable the qubewatchdog. This will prevent windows from locking up and the worker will continue to function. Because qube! 4.0 doesn't have an official 64 bit build yet, the watchdog is currently disabled by default.
Thanks,
Anthony