Hello Richard,
I have a table with a composite primary key (composed of 2 fields). When a unique combination has previously been entered, and a user enters this combination again, they get the standard Microsoft message about violation of PK or duplicate values entered. The message is not too user-friendly or understandable to the users. Do you have a Lesson in which I can make my own message about duplicate values being entered?  I realize it may mean  more than just writing a message, but may require changing the PK in the table.
  THANKS!

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Reply from Richard Rost:

Paula, what you could do is to simply look up this value to see if it already exists. You would need a BeforeUpdate event and something like a DLOOKUP statement. See this tutorial for help with DLOOKUP. I covered it in Access 302, which I see you own. Just look up the value and then if it exists already, pop up a warning message with a MsgBox.