Thanks for responding...I'm getting the same message that I got at first..."The file may be read-only, or another user may have it open. Please save document with a different name, or in a different folder."
The next day I emailed the file to my work PC and encrypted it with no problems. I have WIN 7 and am using Acrobat 8.0 there. So the problem seems to be with my new PC here at home (i.e. WIN 8.1 and Acrobat XI). Frustrating. I'm betting its some obscure setting in WIN or Acrobat, that is way over my head. Please let me know if you have any ideas. Thanks again.
Phil