Informix Error -426: Unknown values have already been supplied.

Reasons / Common Causes

-426 is documented, like -392/-403, as an internal error that shouldn't normally occur under ordinary usage — the official guidance gives no specific application-level trigger, only that this reflects an unexpected internal condition.

1. An internal server-side bug triggered by a specific, likely unusual combination of statement structure and data.
2. A client/driver-level issue interacting badly with the server in a way that produces this internal condition.

Solutions / Resolution

1. Don't expect to encounter this under normal usage, per the official guidance.
2. If it recurs, document the exact circumstances — the statement being executed, client driver/version, server version, and any other conditions present at the time.
3. Contact IBM Informix Technical Support with that documentation, per the official guidance, rather than attempting to diagnose or work around it at the application level.

Examples

Documenting the circumstances for a support case

- Exact statement being executed
- Client driver and version
- Server version
- Frequency: one-off or reproducible?
- Any other errors or anomalies around the same time

Diagnostic Checks

1. Confirm whether the error is a one-off or reproducible.
2. Check the server version against known issues/patches for this specific internal error.

Related Errors / Related Topics

• -392 — "System error - unexpected null pointer encountered." Another error explicitly documented as internal, in the same general server-internal-condition family.
• -403 — "The size of a received row disagrees with the expected size." Another internal communications-level error.

This is documented as an internal error, not a query-writing mistake — if it recurs, gather detailed reproduction information and escalate to IBM Informix Technical Support rather than searching for a SQL-level fix.