That's easy enough to handle. You need to check if the file exists before attempting to add it e.g.
For x = 1 To 5
If FileExists("C:\EmailMsg\" & strAttach & x) Then
objMail.Attachments.Add ("C:\EmailMsg\" & strAttach & x)
End If
Next x
This uses the following function in the same module to establish whether the file exists.
Private Function FileExists(filespec) As Boolean
Dim fso As Object
Set fso = CreateObject("Scripting.FileSystemObject")
If fso.FileExists(filespec) Then
FileExists = True
Else
FileExists = False
End If
lbl_Exit:
Exit Function
End Function