attempted upgrade to b13 "aborts prematurely"

I attempted to upgrade b10 again (to b13 this time) by:

1) downloading b13 in a new directory
2) copying over /sites/default/settings.php from b10 installation
3) reconfiguring settings.php to use a copy of the b10 database
4) copying over /sites/default/files from b10 installation
5) running /update.php - which reported the process was aborted prematurely:

Drupal database update
warning: reset() expects parameter 1 to be array, null given in /Library/WebServer/websites/openscholar_2.0-BETA13/update.php on line 313.
warning: array_pop() expects parameter 1 to be array, null given in /Library/WebServer/websites/openscholar_2.0-BETA13/update.php on line 313.
The update process was aborted prematurely while running update # in .module. All errors have been logged."

I tried running update.php several times again just in case, but each aborted prematurely as above. On the "updated" site, attempting to click on any front page 'featured' links to user-sites (such as http://www.server.com/node/3 which redirects to http://www.server.com/username/) results in a "page not found" error as it has with all of my previous attempts at updating OpenScholar. So far I have tried updating our OpenScholar installation from b10->b11, b10->b12, and b10->b13, all without success, and am starting to fear that it simply cannot be safely updated. Any suggestions regarding where to look next or how this might be resolved would be greatly appreciated - thanks.