If you got this error, “The specified file could not be written to. It may be in use”, try to save the exported file in a different folder. That generally solves the issue. If you have any other error, try saving the file in a different folder with the Word 97 - 2003 Document format.
Also don't expect 100% perfect results. Keep your InDesign layout simple and the resulting MS Word document should need only a little re-working.