KB Article: http://support.microsoft.com/kb/928890
When you try to open a publication in Microsoft Publisher, you may
receive one of the following error messages, depending on the version of
Publisher that you are running:
Microsoft Publisher 2000:
Publisher cannot open
this file. This is not a Publisher file.
Microsoft Publisher 2002 or Microsoft Office Publisher 2003:
Publisher cannot open the
Microsoft Office Publisher 2007:
Publisher has detected a
problem in the file you are trying to open. To protect your computer, Publisher
will not open the file.
To verify the error message that you receive, press CTRL+SHIFT+I.
The following number is displayed in the lower-right corner of the error
message dialog box: