[sqlite] How should virtual table module return its own error messages?

[Evans, Mark (Tandem)]

Greetings,

I followed one of the wiki notes on how a virtual table module method
such as xUpdate should set error message for consumption upstream.  A
code snippet is:
...
        sqlite3_free(aVTab->zErrMsg);
        aVTab->zErrMsg = sqlite3_mprintf( "No such FOO: %s", foo );
...

where aVTab points to sqlite3_vtab.

But my message gets ignored and replaced with stock error message
associated with the return code such as:

        "SQL logic error or missing database"

Did I follow an obsolete note?  Is it possible to do what I want?  Is
there a special return code I should return in such cases rather than
SQLITE_ERROR?

Many thanks,
Mark