Site keeps crashing after Plugin Upgrades

Hi. WP recently did an auto-upgrade on our site - http://www.SAPeople.com - and so we are in the process of upgrading our plugins.

When we the tried to upgrade the Avatars for Multisite Plugin - the entire site (front & back) crashed and our server guys had to rollback the site.

We then did all our upgrades again, this time leaving out the Avatars one...but after upgrading the Post Indexer - our Admin pages are no longer visible. Just entire blank screens.

Pls could you let me know why this may have happened and what we should do to resolve it?

Thanks!