ERROR_INVALID_TASK_INDEX - 1551 (0x60F)
The specified task index is invalid.
Updated: Feb 21, 2026
Technical Meaning
The ERROR_INVALID_TASK_INDEX error code indicates that a task index provided to an API function is not valid. This can occur in scenarios where tasks are managed or manipulated using specific indices, and the index supplied does not correspond to any existing task.
Error Details
- Error Name: ERROR_INVALID_TASK_INDEX
- Numeric Code: 1551 (0x60F)
- Short Description: The specified task index is invalid.
This error typically arises when an application or system function attempts to reference a task using an index that does not exist within the context of the operation being performed. For example, if a task management API expects an index ranging from 0 to N-1, and an index outside this range is provided, this error will be returned.
Usage Context
This error can occur in various contexts where tasks are managed or manipulated using indices. Common scenarios include:
- Task scheduling APIs
- Process management functions
- Thread management operations
The context of the operation determines the valid range for task indices and the conditions under which this error might be returned.
Developer Interpretation
When encountering ERROR_INVALID_TASK_INDEX, developers should ensure that the provided task index is within the expected range. This includes validating input parameters, understanding the scope of tasks managed by a particular API, and ensuring that operations are performed in an appropriate context where valid indices are used.
Developers should also consider the following best practices:
- Validate all input parameters before calling APIs that manage tasks.
- Consult documentation to understand the range of valid task indices for specific APIs.
- Ensure that any operations involving task management are performed within the correct scope and context.
Related Errors
ERROR_INVALID_PARAMETERERROR_OUT_OF_INDEX_RANGEERROR_BAD_LENGTH
These errors often share similar contexts where invalid input parameters or out-of-range values lead to failure in API functions.
FAQ
Q: What does the ERROR_INVALID_TASK_INDEX error mean?
A: It indicates that a task index provided to an API function is not valid, meaning it falls outside the expected range of indices for the operation being performed.
Q: How can I avoid this error?
A: Validate all input parameters and ensure they fall within the expected ranges as documented by the specific APIs you are using. Always consult the documentation for correct usage contexts.
Summary
ERROR_INVALID_TASK_INDEX is a specific error code indicating that an invalid task index was provided to an API function. Developers should validate their inputs and understand the valid range of indices for the operations they perform to avoid this error.