Test for 1 occurances meet same criteria. Display address in MsgB
 

In Sheet1 I want to test col. W for more than one occurances of the same text
value and at the same time both/all matches a constant text value in col. P
on the same row. The criteria/text in col P is: "Started". The values in col.
W are picked through validation from a named range called "Cell_No-Prod". The
text is: "Cell1", "Cell2",...."Area1", "Area2",.....etc.

I want to display a MsgBox with the text: "You have entered [text value from
W] [n] times. Max allowed is one. Please correct. The repeated entry are in
row [row numbers]."

The user shall be able to close the MsgBox, correct the wrong entry, before
a new warning goes off. 3 minutes would be enough.

I know how to make user forms, but I'm stuck on the code/test for repeating
values.
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Thanks
John