Maybe you done what I just made : remove a folder which was in your Finder sidebar. Now you can’t remove from it.
So here is the solution which require Xcode installed.
In your terminal do
Or open this file manually.
You should have « Property List Editor » app to do this.
Open each entries to find what you want under Root » useritems » CustomListItems. Try to open each item and check the name of the folder. When you found the correct entry, delete the « Item x » and save the file.
When it’s done, just restart Finder.
Or just make option+click on Finder’s icon in your dock, then Relaunch.
It’s that simple :)