I have the same problem when I try to open a PDF file with internet explorer. It says "The Acrobat/Reader that is running can not be used to view PDF files in a Web Browser." The error says it can't connect to a DDE server.
None of the "fixes" actually fix the problem.
Process explorer shows the Acrobat process running (multiple times if I've tried to open it multiple times) but none of them are visible in windows.
Acrobat works by itself on locally stored files.