After you assign the [Shipped Date], in one way or the other, you can check to see if the shipments exceed your limit for a given date with something like this
Code:
If DCount("*", "ActualTableName", "[Shipped Date]= #" & Me.[Shipped Date] & "#") > 2 Then
MsgBox "More than 2 Items Scheduled to Ship on This Date!"
Exit Sub
End If
The sample code will pop the Messagebox if there are 3 or more shipments already scheduled for the given date, and exit the Sub, without carrying out the rest of the code, such as saving the Record. This would allow you to try a new shipping date.
You can adjust 2 to fit your needs, of course, and replace ActualTableName with the actual name of your Table.
Linq ;0)>
The problem with making anything foolproof...is that fools are so darn ingenious!
All posts/responses based on Access 2003/2007