User1239191831 posted
Thanks for the advice all.
In the end I coded around the issue by putting the setting the SQL Select parameter to a Session variable. This allowed me to validate the value in my VB code before moving it into the Session var. Not that elegant, but it works.
if it doesn't work then alert with message box and set focues to cleared textbox for them to enter again
Not possible, even if I use a Javascript messagebox as the postback triggers the SQL select before the msgbox will be displayed on the client.