Macro Cycle Through Open Workbooks

I am trying to cycle ALL open workbooks so that I can choose the file to manipulate in subsequent code this is the code that I am utilizing furhter below

this is my code

VB:

For Each wb In Workbooks
If MsgBox("Do you want to do access this Workbook for the Update " & Chr(10) & Chr(10) & wb.Name, vbYesNo) = vbYes Then
wb.Activate
VI_wb = wb.Name
I = True
End If
Next wb

But for some reason it only loops through .xls and xlm workbooks BUT not .xlsx

is there a way that I can loop through any and all open workbooks.

The reason I do this is because my update are based on many numerous excel workbooks with differnet extentions, and naming conventions and many of the come via email, I cannot use the eact naming convention