Strange Date Behaviour

[Thomas Hidderley]

I have several databases with date fields. The format in all of them  
is "MM/DD/YY". The fields have accepted inputs for many years until a  
few days ago. I tried running an action in an invoice database and  
received the message "illegal date".
When I try to input a date in the database in the above format I  
receive the message "Month must be from 1 to 12. Click Re-edit to re- 
edit." So now when I enter the date with DD first followed by MM it  
not only accepts it but re-formats it to the original "MM/DD/YY" .  
However until I change the date format to DD/MM/YY in the action  
procedure I still receive the "Illegal Date" message.
Does anyone have a clue as to what stupid thing I may have done to  
cause this? More importantly how do I correct it? Thanks