steam's cache of installed/downloaded/updates to games can get corrupted and cause this. try the 'clear download cache' option in settings and then restart steam and try to uninstall a game again.
I don't remember where its actual folder is, but Steam creates a link to it in your home folder. ~/.steam/steam should take you there. In there, games are installed in the steamapps folder. If all else fails, you can delete the game's folder from there.
This is assuming the game in question is installed on the same drive as Steam.