I am having the exact same problem. However I upgraded from Word 2008 to Word 2011 in Mac OS X Lion.

The sources.xml file is there - with all my citations in there. However it isn't being used by Word 2011 because when I open word and look at my master list... bam! it's empty!

I tried searching for files which have been modified today hoping I might chance upon where Word 2011 stores the master citation list but I haven't had any luck finding it.

Has anybody had any success? I really don't want to start typing in my citations from scratch again.