From "Help" on Data Validation ....

Messages appear only when data is typed directly into the cells. Your
message won't appear:

When a user enters data in the cell by copying or filling.
When a formula in the cell calculates a result that isn't valid.
When a macro (macro: An action or a set of actions that you can use to
automate tasks. Macros are recorded in the Visual Basic for Applications
programming language.) enters invalid data in the cell.


"Ruben" wrote:

I've tried to put data validation on a cell that gets its value from another
cell, in another worksheet. When the value changes, data validation does'n
kick in. How come?
This is my example: cell A1 in sheet2 is equal to B2 in sheet1, I put data
validation on cell A1 in sheet2. When the value in B2 sheet1 changes, it also
changes in A1 sheet2 but the my validation is not followed and no pop up box
appears.

Any info would be helpful, thanks!