I've noticed since installing OS X Mavericks Developer Preview 6, I can no-longer access USB devices from Windows 7. When I try, I get a little pop-up that says "Unable to connect the USB device to your virtual machine. The device cannot be connected now. Please try again later." Problem ID: 471
Having the exact same issue with all Parallels VM sessions - Windows 7, Windows XP, Windows 8.. Everything worked just fine in DP5. Currently, I only see the USB errors mentioned above, for all USB devices, on any VM.
I do have the some problem running with a XP SP3 guest. Re-install cleaning out parallels tools and re-install of them did not help.
Installed VMWare Fusion and converted my Parallels VM(s) (took a couple hours). Everything is working with VMWare and DP6.
The first release of PD9 has this bug. People also report it also happen in mountain lion. Can't believe how they let this one pass