из Microsoft Visual Basic Help:
quote:
The BeforeDocumentSaveAs event fires when a document is saved to either a native format (for example, VSD or VDX) or a non-native format (for example, HTM or BMP). It does not fire when a document is saved to DWG, DXF, and DGN formats. To save a document in a non-native format programmatically, you must use the Export method of the Page object.
попробуй заменить
Application.ActiveWindow.Selection.Export "K:\sx\" & num & ".dwg"
на
Application.ActivePage.Export "K:\sx\" & num & ".dwg"