loop counter not recognised

Please can someone help with the below code? I am trying to write this to check whether a workbook is already open by another user but it gets stuck in the loop and ignores (or more probably my code is wrong) the counter which should cause an "Exit Do" at a value of two -

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Also I realise this is perhaps the wrong approach for my solution. Is there a way of determing read only status without opening the workbook?

Many thanks

Dave