Knowledge

ERROR_OPLOCK_NOT_GRANTED - 300 (0x12C)

The oplock request is denied.

Updated: Feb 21, 2026

Technical Background

Oplock, or Opportunistic Locking, is a feature in the Windows file system that allows files to be locked and unlocked on behalf of a client. This can improve performance by reducing network traffic and allowing clients to cache file data locally. The ERROR_OPLOCK_NOT_GRANTED error indicates that an attempt to establish an oplock was denied.

Error Details

The ERROR_OPLOCK_NOT_GRANTED error is returned when the system cannot grant an oplock request made by a client. This can occur for various reasons, such as exceeding file system limits or encountering unsupported operations.

Common Causes

  • Exceeding Limits: The number of outstanding oplocks may have been exceeded, preventing additional requests from being granted.
  • Unsupported Operations: Certain file operations might not support oplock requests, leading to the denial.
  • Client-Side Issues: Client-side issues such as incorrect parameter values or corrupted data can also result in this error.

Real-World Context

This error typically occurs during file access operations over a network. For example, when a client attempts to open a file for exclusive use, the server might deny the oplock request if it cannot guarantee that no other clients will concurrently modify the same file.

Is This Error Critical?

The criticality of this error depends on the specific operation and context. While not necessarily catastrophic, it can impact performance and user experience by preventing efficient file access over the network.

How to Diagnose

  1. Review Operation Context: Ensure that the operation is being performed in a valid context where oplocks are supported.
  2. Validate Parameters: Check for any invalid parameter values or corrupted data that might be causing the denial.
  3. Confirm Object Types: Verify that the file operations are being applied to the correct types of objects (files, directories).
  4. Verify Input Data: Ensure that all input data is valid and meets the required constraints.
  5. Check Limits or Constraints: Confirm that the system has not reached any operational limits that could prevent oplock requests from being granted.

How to Resolve

  1. Correct Parameter Usage: Ensure that all parameters are correctly specified and within allowable ranges.
  2. Adjust Operation Context: If possible, adjust the operation context to ensure it aligns with supported file system operations.
  3. Restore Data: If data corruption is suspected, restore or repair any corrupted files or directories.
  4. Retry Operation with Valid Inputs: Attempt the operation again with valid inputs and a proper understanding of the oplock requirements.

Developer Notes

  • Oplock Support: Ensure that your application supports oplocks where they are applicable to improve performance.
  • Error Handling: Implement robust error handling to gracefully manage ERROR_OPLOCK_NOT_GRANTED errors, providing feedback to users or logging appropriate messages.

Related Errors

FAQ

Q: What does the ERROR_OPLOCK_NOT_GRANTED error mean?

A: It indicates that an oplock request was denied, likely due to exceeding limits or unsupported operations.

Q: How can I prevent this error from occurring?

A: Ensure proper parameter validation and operation context. Avoid exceeding system limits for outstanding oplocks.

Q: Can this error be critical?

A: While not necessarily catastrophic, it can impact performance by preventing efficient file access over the network.

Summary

The ERROR_OPLOCK_NOT_GRANTED error is a specific technical issue related to file operations in Windows. It indicates that an oplock request was denied due to various reasons such as exceeding limits or unsupported operations. By understanding its context and implementing appropriate diagnostics and resolutions, developers can ensure smoother network file access.