I'm using SmartGit. I want to ignore a folder in repository. When I right-click folder, option "Ignore" is grayed out and I can't click it.
You would need to make sure this folder content isn't versioned first.
In command line, try a git rm --cached -r yourFolder/
Then check if the ignore option is now available.
The other reason would be because that folder is empty. since Git doesn't track empty folder, maybe SmartGit doesn't allow to ignore it.