I recently uninstalled OwnCloud and the icon remains in the sidebar of windows explorer and will provide a “location is not available” error when clicked. I am assuming I need to edit something in the registry like you do to remove the icons for OneDrive or Dropbox, but I am not sure what the keys are.
If you have removed the windows synchronization client but still have the owncloud shortcut or symbol in the windows navigation side bar,
here is how you can remove it:
Open regedit. (press the Windows Key and type regedit)
Search (CTL+F) for the name of the client, in this case owncloud.
Press F3 for next search result.
Look for the key System.IsPinnedToNameSpaceTree.
Right click on the key name, change, set to 0 instead of 1.
You have to do this twice. Once for the x64 and x32 system settings.
Once this is done, you don’t even need a reboot, just open and close your explorer - the sidebar is clean.