Site keeps crashing after Plugin Upgrades

Hi. WP recently did an auto-upgrade on our site - - 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?