ERROR_NOTIFICATION_GUID_ALREADY_DEFINED - 309 (0x135)
The specified file already has a notification GUID associated with it.
Updated: Feb 21, 2026
Technical Meaning
The error code ERROR_NOTIFICATION_GUID_ALREADY_DEFINED indicates that a notification GUID has already been assigned to the specified file. A notification GUID is used in Windows for identifying and managing notifications related to files or directories.
Error Details
This error typically occurs when an attempt is made to assign a notification GUID to a file that already possesses one. Notification GUIDs are unique identifiers used by the operating system to manage events such as changes in file attributes, access requests, and other file-related operations.
Usage Context
This error can arise in scenarios where applications or system components attempt to register notifications for files or directories. It is particularly relevant when dealing with file monitoring or change notification mechanisms provided by Windows APIs like FindFirstChangeNotification or ReadDirectoryChangesW.
Developer Interpretation
When encountering this error, developers should ensure that the file in question does not already have a notification GUID associated with it before attempting to register for notifications. This can be achieved by first checking if a GUID is already assigned and handling the situation appropriately based on the application's requirements.
Related Errors
ERROR_NO_GUID_TRANSLATION(1208)ERROR_FILE_NOT_FOUND(2)ERROR_PATH_NOT_FOUND(3)
FAQ
Q: What does this error mean?
A: This error indicates that a notification GUID is already defined for the specified file.
Q: How can I handle this error in my application?
A: Ensure that you do not attempt to assign a notification GUID to a file that already has one. Check if the GUID is assigned before proceeding with registration.
Summary
The ERROR_NOTIFICATION_GUID_ALREADY_DEFINED (309) error signifies that an attempt was made to assign a notification GUID to a file that already possesses one. Developers should ensure proper handling of such cases in their applications to avoid this error and maintain system stability.