VMware fusion 4 won't launch due to out of date, running guests When running the Upgrade Installer from VMware Fusion 3.1.3 to v4.0.1, this dialog pops up:

A virtual machine is running with an older version of VMware Fusion.
Please use the older version of VMware Fusion to suspend or power off all virtual machines.

I shut down all the guests, reran the installer, same thing. I used vmware article 1017838 to uninstall v3 manually, reboot, and then drag the Fusion 4 app to the Applications folder. Reboot and run Fusion. Same thing. Checked /var/run for vmware items. Checked Activity Monitor for vmware items. Rechecked locations specified in 1017838 and used spotlight to search around.
I moved all my guests to an extra drive and unmounted that drive, and repeated the uninstall and reinstall.  A friend recommended an app called &quot;CleanApp&quot; to watch what files are created and modified during the installs, which did reveal a bit more cruft. Basically, I've tried to scrub my system of all things Fusion, both versions including guests, and then done a reinstall, and that hasn't worked. My last gasp was booting into the 32 bit kernel but that didn't help.
I've filed a ticket with VMware, but it's been a slow slog.
You can try with this command from a Terminal:

VMware 3.x

/Library/Application\ Support/VMware\ Fusion/vmrun list 

VMware 4.x

/Applications/VMware\ Fusion.app/Contents/Library/vmrun list

to see if you have any VMs runnig - if you do, then run this command:

VMware 3.x

/Library/Application\ Support/VMware\ Fusion/vmrun -T fusion stop "/path/to/.vmx" hard 

VMware 4.x

/Applications/VMware\ Fusion.app/Contents/Library/vmrun -T fusion stop "/path/to/.vmx" hard

where you replace "/path/to/.vmx" with your path to the VM still running.