Have you accidently toggled Document Protection.
Are you using a trial version that has reached its number of days and needs
activating.
Or follow Suzanne's advice pasted below.
The message you are getting is probably something like "This modification is
not allowed because the document is locked." One reason could be that the
document is protected; see "You receive a 'This modification is not allowed
because the document is locked' error message when you modify a document in
Word 2007 or in Word 2003" at
http://support.microsoft.com/?kbid=818852.
If the message is "This command is not available because the document is
locked for editing," see
http://support.microsoft.com/?kbid=930698.
Hope this helps,
