I have had problems in the past using phpMyAdmin to export a database dump. I suggest that you try to do a mysqldump from the command line and see if you get better results. I have found that phpMyAdmin times out too quickly during a dump, and I don't get good results.
Bob -- Robert L. DeSilets, Jr. Sr. IT Support Specialist ISC-CSG desilets@isc.upenn.edu (215)898-0067