What does Windows error code 156 (ERROR_SIGNAL_REFUSED) mean?

ERROR_SIGNAL_REFUSED

What ERROR_SIGNAL_REFUSED means

The target process refused the signal sent by the caller. This legacy process-control result represents an explicit rejection, not inability to locate the process. The target exists but is unwilling or unable to accept the requested signal under its current state or policy.

Common causes

• The target disabled handling for that signal
• The process is shutting down or in a protected state
• The signal is not valid for the target execution mode
• A compatibility layer rejects cross-session or cross-subsystem signaling

How to investigate

1. Record the target process, signal number, session, and caller identity
2. Check the target state and registered handlers
3. Verify the signal is supported by the target subsystem
4. Test a benign signal against the same target to separate policy from state

Developer guidance

Treat refusal as a defined response. Do not escalate immediately to forceful termination; provide a timeout, alternate control channel, and clear audit logging.

Administrator and support guidance

Check whether security, session isolation, or service policy intentionally blocks the operation before changing permissions.

How this code differs from related results

ERROR_NO_SIGNAL_SENT means no eligible handler was reached; refusal means the target actively declined or could not accept the signal.

References

• Microsoft: System error codes 0–499