I've been having constant problems with Windows 7-64. I'm seeing locks on startup, locks on tools menu, and locks on open serial port. Uploading seems to take longer too.
I've tried changing reinstalling the latest drivers from FTDI's site, as well as changing the serial port. I'm still having the same problem.
[I know that Windows 7-64 is a stinking festering RAM-eating pile of bloated NSA-endorsed excrement that became the emperor's new clothes, but I still need to use it for a few things....]