What does Windows error code 106 (ERROR_SEM_USER_LIMIT) mean?

ERROR_SEM_USER_LIMIT

What ERROR_SEM_USER_LIMIT means

ERROR_SEM_USER_LIMIT is a Win32 system result whose documented message is: “Insert the diskette for drive %1.” In practical troubleshooting, it belongs to legacy semaphore accounting, typically in OS/2 or DOS-derived compatibility behavior, where a per-user or subsystem semaphore limit has been reached.

Typical causes

• the application creates named semaphores without closing them
• many instances share a finite semaphore table
• an abnormal termination leaves compatibility-layer semaphore state allocated until the subsystem resets

How to investigate the result

1. count named synchronization objects created by each process instance
2. Compare one-process and many-process reproduction
3. Verify that failure disappears after the owning process or compatibility subsystem exits

Developer guidance

Reuse synchronization objects where possible and close them deterministically. A retry loop that creates another semaphore increases the pressure and should be avoided.

Administrator and support guidance

Limit duplicate application instances and collect object counts before terminating them. If a single instance steadily increases the count, route the evidence to the application owner.

Example

A legacy client creates a fresh named semaphore for every request. After enough requests, the subsystem refuses another semaphore with this result.

How it differs from related results

This is not a timeout while waiting on a semaphore; it means creation or allocation cannot proceed because the permitted semaphore population is exhausted.

References

• Microsoft: System error codes 0–499