action=info gives

The action specified by the URL is not recognized by the wiki

(when $wgAllowPageInfo=false.)

But this is the same response as when e.g., action=zzzzzzzzz.

Therefore say

The action specified by the URL is disabled by the wiki

Yes, it will complicate your algorithm, but that's what I'm here for :-).

Version: 1.9.x
Severity: minor
OS: Linux
Platform: PC