LOL, easist (safest) solution that I've found when I got that message was to reboot.

You can also do the following
- Logout of any active SB sessions you have open,
- shutdown the SB service,
- kill any remaining SB related stuff hanging around
- startup the SB service.
But if you get more weird issues; then you will reboot.

SB is very finicky and uses a lot of behind the scenes "voodoo" to perform its magic, including mounting folders into other folders. And I've seen it get into a weird state where the sb service is partially working after a simple service restart.

So, the safest "solution" that I always use has been just restart the virtual machine I use..

Nathan.