Informix Error -581: Error loading message file.

Reasons / Common Causes

-581 fires when SET EXPLAIN can't complete because the server can't find its message-template file, used to format the explanatory query-plan output — an installation-level problem, per the official guidance.

1. A missing or relocated message-template file in the Informix installation — per the official guidance's framing, this is squarely an installation issue.
2. INFORMIXDIR (or an equivalent installation-path setting) misconfigured, pointing at an installation missing this file, similar in nature to the -553/-558 missing-executable family.
3. An incomplete or partially-upgraded Informix installation, where some components (like the message-template file) weren't updated or installed alongside others.

Solutions / Resolution

1. Consult with the person who installed the IBM Informix software, per the official guidance — this is the documented remediation path, since the fix is installation-level, not something to work around from SQL.
2. Check INFORMIXDIR as a first troubleshooting step, similar to the -553/-558 pattern, to confirm the connection is pointed at the intended, complete installation.
3. Avoid SET EXPLAIN until the installation issue is resolved, since this specific functionality depends on the missing file.

Examples

Checking the installation path first

$ echo "$INFORMIXDIR"

Confirm this points at the intended, complete installation before escalating to whoever manages it.

Diagnostic Checks

1. Confirm INFORMIXDIR points at the intended installation.
2. Escalate to the installer/administrator if the path is correct but the message-template file is still missing — this isn't resolvable from the application/SQL side.

Related Errors / Related Topics

No closely related error codes are cross-referenced for -581 in this set yet.

An installation-level problem specific to SET EXPLAIN — escalate to whoever installed the software rather than trying to work around it from SQL.