[Gauthier]

Browsing for Calibre, current version always goes to the parent.
don't know why really...

Correction, pick the dir of the executable using a file picker instead:
in frmCalibreAllFormat Add:

Private Function BrowserCalibre()
    On Error GoTo Err_Clr

    Dim bDisplayVal As Boolean
    Dim szDocName As String
    Dim szPath As String
    Dim defpath As String
    
    bDisplayVal = False
       
    With Application.FileDialog(msoFileDialogFilePicker)
        .AllowMultiSelect = False
        .Title = "Please select The Calibre Executable"
        .Filters.Clear
        .Filters.Add "Applications", "*.EXE"
        
        bDisplayVal = .Show
        szPath = CurDir
    End With

    If bDisplayVal = -1 Then
        BrowserCalibre = szPath
    End If
    
    Exit Function
    
Err_Clr:
    If Err <> 0 Then
    Err.Clear
    Resume Next
    End If
    

End Function

and change

Private Sub cmdPathtoCalibre_Click()
    txtCalibrePath.Text = BrowserCalibre
End Sub