This works on Mac OS X for sure, but I suspect if you can find the right files on Windows it’s the same fix.

1. Quit Yammer.
2. Open Terminal
3. type: rm -rf ~/Library/Application Support/Adobe/AIR/ELS
4. type: rm -rf ~/Library/Preferences/Yammer*
5. Relaunch ze Yammer.

If you like what’s here, please follow me on twitter here.