"There are other users logged on to this computer."

"There are other users logged on to this computer.

If you uninstall this program while another user is running it, the program might not uninstall completely."

I'm working on a server that is currently out of space.  So I'm going through programs and seeing what I can uninstall when I get that message about other users being logged in and the uninstall might not run correctly.
So I tried to log off, and couldn't.
I checked with everyone else and no one was logged into the server.
I found that I can see who is logged in through the Terminal Services Manager
(click Start, click Control Panel, double-click Administrative Tools, and then double-click Terminal Services Manager. (and yes I'm a noob))
I was able to log everyone off (there was one disconnected session) and continue with my uninstallation.  This time no error.
To log off the other user, you simply right click the user and select Log Off.
This may have happened by disconnecting RDP sessions instead of logging off first.
Hope this helps someone out there!