This happens when you have this .wzfolder document file marked as read-only in the file system. Note the document location at the top. Open Windows Explorer and go to that folder. Select the .wzfolder document file and right-click to see the properties. Uncheck the Read Only attribute and you are all set to be able to edit it again in WhizFolders.
If the above properties shows that Read Only is already off then the reason might be that this file is already opened by another application or another user on the network. For example, if someone is viewing it with WhizFolder Viewer, WhizFolders will automatically open it Read Only.