Syntax: select box
Show Error Messages determines the disposition of error messages during searches. It may be set to one of the following values:
None 
    Suppress all errorsIn HTML comments 
    Show errors in HTML comments (for HTML results styles) so that
    they are not normally visible to the user, but can be viewed
    via View Source in a browser.  In XML results styles, errors
    will be suppressed.In HTML comments & query errors visible 
    Show errors in HTML comments (for HTML results styles),
    but show query-related errors (e.g. "Your query was all
    noise words.") visibly (in gray boxes).
The default is In HTML comments & query errors visible. Note that in admin (test search) mode, all errors are always shown visibly, for admin perusal.