The following Function has been designed to check if a workbook you are about to open is already open. If it is then it will return TRUE, if not then the Function will return FALSE and your other Macro code should then open the workbook that is required.
'Will verify if a Workbook is open before trying to open it
Dim wb As Workbook
IsWorkbookOpen = True
On Error Resume Next
Set wb = Workbooks(wbName)
If wb Is Nothing Then IsWorkbookOpen = False
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