Knowledge

ERROR_CANNOT_GRANT_REQUESTED_OPLOCK - 801 (0x321)

An oplock of the requested level cannot be granted. An oplock of a lower level may be available.

Updated: Feb 21, 2026

Technical Background

Oplocks, or opportunistic locks, are a mechanism in the Windows file system that allows clients to cache file data locally. This reduces network traffic and improves performance by allowing files to be locked without explicit locking requests from the client.

Error Details

The error ERROR_CANNOT_GRANT_REQUESTED_OPLOCK (801 or 0x321) indicates that a higher-level oplock request could not be granted due to system constraints. This typically occurs when the file server cannot provide an oplock of the requested level, and an oplock of a lower level may be available.

Common Causes

  • Invalid Parameter Values: The client or server might have specified an unsupported oplock level.
  • Exceeding Limits: There could be limitations on the number of concurrent oplocks that can be granted by the file system or network stack.
  • Corrupted Data: In rare cases, corrupted metadata related to oplocks might prevent their proper granting.

Real-World Context

This error is commonly encountered in scenarios involving high-performance file sharing over a network. It often arises when multiple clients attempt to access and cache the same files simultaneously, leading to conflicts that cannot be resolved with higher-level oplocks.

Is This Error Critical?

The criticality of this error depends on the specific application scenario. In most cases, it is not a catastrophic failure but rather an indication that lower-level oplocks will be used instead, which may impact performance.

How to Diagnose

  1. Review Operation Context: Ensure that network and file system configurations are correct.
  2. Validate Parameters: Check the parameters passed during file operations for any invalid values.
  3. Confirm Object Types: Verify that the operation is being performed on a supported object type (file or directory).
  4. Verify Input Data: Confirm that all input data, including oplock levels, are valid and within expected ranges.
  5. Check Limits or Constraints: Ensure that there are no system-wide limits that could be causing this issue.

How to Resolve

  1. Correct Parameter Usage: Adjust the parameters used in file operations to ensure they are within supported ranges.
  2. Adjust Operation Context: Modify network and file system configurations if necessary to support higher-level oplocks.
  3. Restore Data: If data corruption is suspected, restore from a backup or correct any issues with the metadata.
  4. Retry Operation with Valid Inputs: Attempt the operation again using valid inputs that do not exceed supported limits.

Developer Notes

Developers should be aware of the limitations and constraints associated with oplocks when designing networked file access operations. Ensuring proper validation and error handling can help mitigate issues related to ERROR_CANNOT_GRANT_REQUESTED_OPLOCK.

Related Errors

FAQ

Q: What does the error ERROR_CANNOT_GRANT_REQUESTED_OPLOCK mean?

A: This error indicates that a higher-level oplock request could not be granted due to system constraints, and an oplock of a lower level may be available.

Q: How can I prevent this error from occurring?

A: Ensure proper validation of parameters and input data. Adjust network and file system configurations as needed to support higher-level oplocks.

Q: Is this error critical for my application?

A: The criticality depends on the specific scenario. In most cases, it is not a catastrophic failure but an indication that lower-level oplocks will be used instead.

Summary

The ERROR_CANNOT_GRANT_REQUESTED_OPLOCK (801 or 0x321) error in Windows indicates that higher-level oplock requests could not be granted. This typically occurs due to system constraints and can be mitigated by validating parameters, adjusting configurations, and ensuring proper input data.