Call to undefined function jquery_update_get_replacements()

On one of my sites with Advagg I just got an WSOD plus numerous fatal errors in Apache's error log:

fatal error a:

[Wed Jan 18 23:29:02 2012] [error] [client xxx] PHP Fatal error: Call to undefined function jquery_update_get_replacements() in /var/www/drupal/sites/all/modules/advagg/advagg.module on line 833 ...

and fatal error b:

[Wed Jan 18 23:31:09 2012] [error] [client xxx] PHP Fatal error: Call to undefined function jquery_update_get_replacements() in /var/www/drupal/sites/all/modules/ctools/ctools.module on line 485 ...

This happened immediately after resolving a security issue with the 'quicktabs' module: #1409608: WSOD after updating security update (DRUPAL-SA-CONTRIB-2012-012 ). Disabling Advagg does not resolve the issue. As soon as Advagg is disabled, the fatal errors of type b occur, those of type a disappear.

I have no idea what is going on here; I checked the site before the 'quicktabs' update, and it worked smoothly.

Any ideas or suggestions?