VFP automatically displays INVALID INPUT message if you return FALSE from a VALID method. This bothers some developers because they would like to write their own error messages. You can put your own message in the VALID routine but you get the automatic INVALID INPUT message also. Two messages ? I don't think so.
Solution ? Turns out to be quite simple.
Put SET NOTIFY OFF in your main program (or anywhere prior to where it will be needed) and PRESTO !!! Done ! No more automatic INVALID INPUT messages.