the following solution calls the first macro to check for dups, and if
they're found, calls the second macro to ask the "Yes or No" question. call
the first macro from the control's BeforeUpdate event.
MacroName: CheckForDups
<use the following condition if MyFieldName is a numeric data type.>
Condition: DCount("[MyFieldName]", "MyTableName", "[MyFieldName] = " &
MyControlName) > 0
<if MyFieldName is a text data type, use the condition below *instead of*
the one above.>
Condition: DCount("[MyFieldName]", "MyTableName", "[MyFieldName] = '" &
MyControlName & "'") > 0
Action: RunMacro
MacroName: AskQuestion
MacroName: AskQuestion
Condition: MsgBox("This is a duplicate value. Do you want to enter
it?",4)=7
Action: CancelEvent
hth