Bibliography not created

I am using X4.  I have a 1000 page document with the footnotes tagged. For a year or so it has created a bibliology at the end flawlessly.  Suddenly, it no longer works.  It goes through the process and then says Word is not responding and I am to switch or retry. Either option bails out back to the cursor in Word where i wanted the bibliography inserted. I can no longer create a bibliography and do not know why.  I am using Word 2010 on Win 7.