Sometimes SharePoint Designer loses touch with reality – it demands to check out files that are not checked in, refuses to check in other files and generally misbehaves. This demeanor is sometimes accompanied by this error message:
Cannot perform this operation. The file is no longer checked out or has been deleted.
Simply put, SharePoint Designer is out of sync with SharePoint and you have to delete its cache in order to rebuild it. The cache is composed of these 2 folders:
- %APPDATA%MicrosoftWeb Server ExtensionsCache