Here is a little tip on how to remove missing or orphaned nodes within Umbraco. You may encounter this error if you try copying nodes within the back office. You'll receive an error relating to a method called 'umbraco.dialogs.moveOrCopy.CheckPermissions'. To find any orphaned nodes and remove them, run the following script against your Umbraco database. Make sure you backup your database first. It's a little long winded but the script finds any nodes and dependancies that do not have a version, are not trashed and is of type content.
You may encounter a situation where some of your orphaned nodes have child nodes. You'll need to remove these as well. To identify and remove child nodes of orphaned children, use the following script before the script above. Make sure you backup your database.