Query expression and result

[Peter Le]

Thanks to some helps from the members in this list, I am able to load
graphic and data from mapserv.  The only problem is when I click on the map,
the result comes back as :  "getNumeric(): Incorrect data type"  ...what
does this mean?
Also, in a query syntax, what does the "^-" indicate? i.e., EXPRESSION "^-"
Maybe a book about mapserver is needed :-)   
Thanks,