Workbook Merging and Err Handling

I got this great sub from Ron de Bruin that does everything I need (Almost). The merging function works wonderfully the only thing i have left to figure out is how to add some error handling if a file in the path folder is unable to be opened.

To elaborate, while i was testing the code one of the files ("DetailReport(2)") was able to merge with the others. Upon further investigation the cause was not with the code but in fact when it was downloaded the file was somehow corrupted.
What I would like in someway to not only stop the code but possibly display a messagebox with the file name that couldnt be opened. Any ideas??

 'Clear Master except header
    Sheet4.Rows("2:" & Rows.Count).ClearContents

    Dim MyPath As String, FilesInPath As String
    Dim MyFiles() As String
    Dim SourceRcount As Long, Fnum As Long
    Dim mybook As Workbook, BaseWks As Worksheet
    Dim sourceRange As Range, destrange As Range
    Dim rnum As Long, CalcMode As Long

    'Fill in the path\folder where the files are
    MyPath = Sheet1.Range("C4")

    'Add a slash at the end if the user forget it
    If Right(MyPath, 1) <> "\" Then
        MyPath = MyPath & "\"
    End If

    'If there are no Excel files in the folder exit the sub
    FilesInPath = Dir(MyPath & "Fulfillment*.xl*")
    If FilesInPath = "" Then
        MsgBox "No files found in selected folder"
        Exit Sub
    End If

    'Fill the array(myFiles)with the list of Excel files in the folder
    Fnum = 0
    Do While FilesInPath <> ""
        Fnum = Fnum + 1
        ReDim Preserve MyFiles(1 To Fnum)
        MyFiles(Fnum) = FilesInPath
        FilesInPath = Dir()
    Loop

    'Change ScreenUpdating, Calculation and EnableEvents
    With Application
        CalcMode = .Calculation
        .Calculation = xlCalculationManual
        .ScreenUpdating = False
        .EnableEvents = False
    End With

    'Add a new workbook with one sheet
    'Set BaseWks = Workbooks.Add(xlWBATWorksheet).Worksheets(1)
    Set BaseWks = Sheet4
    
    rnum = 2

    'Loop through all files in the array(myFiles)
    If Fnum > 0 Then
        For Fnum = LBound(MyFiles) To UBound(MyFiles)
            Set mybook = Nothing
            On Error Resume Next
            Set mybook = Workbooks.Open(MyPath & MyFiles(Fnum))
            On Error GoTo 0

            If Not mybook Is Nothing Then

                On Error Resume Next

                With mybook.Worksheets(1)
                    Set sourceRange = .Range("A2:AN1800")
                End With

                If Err.Number > 0 Then
                    Err.Clear
                    Set sourceRange = Nothing
                Else
                    'if SourceRange use all columns then skip this file
                    If sourceRange.Columns.Count >= BaseWks.Columns.Count Then
                        Set sourceRange = Nothing
                    End If
                End If
                On Error GoTo 0

                If Not sourceRange Is Nothing Then

                    SourceRcount = sourceRange.Rows.Count

                    If rnum + SourceRcount >= BaseWks.Rows.Count Then
                        MsgBox "Sorry there are not enough rows in the sheet"
                        BaseWks.Columns.AutoFit
                        mybook.Close savechanges:=False
                        GoTo ExitTheSub
                    Else

                        'Copy the file name in column A
                        With sourceRange
                            BaseWks.Cells(rnum, "A"). _
                                    Resize(.Rows.Count).Value = MyFiles(Fnum)
                        End With

                        'Set the destrange
                        Set destrange = BaseWks.Range("B" & rnum)

                        'we copy the values from the sourceRange to the destrange
                        With sourceRange
                            Set destrange = destrange. _
                                            Resize(.Rows.Count, .Columns.Count)
                        End With
                        destrange.Value = sourceRange.Value

                        rnum = rnum + SourceRcount
                    End If
                End If
                mybook.Close savechanges:=False
            End If

        Next Fnum
        BaseWks.Columns.AutoFit
    End If

ExitTheSub:
    'Restore ScreenUpdating, Calculation and EnableEvents
    With Application
        .ScreenUpdating = True
        .EnableEvents = True
        .Calculation = CalcMode
    End With
End Sub