How to use "CreateObject("WScript.Shell").Popup" in different workbooks at the same time.

Hi XL-experts.
I am new here and I hope you can give me a suitable solution.

I am using the folowing code to show a timed message every 10 minutes. If the user wants to continue working, he must click the OK button.
Else the workbook will close, so others can work with it.
code:

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The code is called after 10 minutes from Sub Workbook_Open().

Nice, all works fine, really perfect.
As long as the user is working with one Excel workbook.
But it is not rare that the user uses 2, 3 4 or even 5 workbooks at the same time, including the same code.

And then it is not working anymore.
The messages keep waiting for each other to pop up and continue.
I have tried so many things to solve it.
It just looks like it is only possible to use 1 pop up function in general and they are "communicating" with each other.

Doe someone knows a solution for this?

mario

BTW, Happy new year to all!

I started creating a user form with a timer code, for the same purpose.
Pop up a message that must be clicked to work on with the spreadsheet.
If not, the spreadsheet will close itself.
This is also working as a charm... well, again for only one workbook.
When 2 or more workbooks are opened at the same time, the last workbook takes over the prior messages.
When that message is clicked to work on, the prior messages disappear and will never come back, without closing any workbook.
It looks like the timer function is dedicated to only one workbook......