I initially got the following error when I tried to activate hummingbird:
Fatal error: Wrong parameters for Exception([string $exception [, long $code ]]) in /home/wagwashg/public_html/wp-content/plugins/wp-hummingbird/core/api/class-wp-hummingbird-api-exception.php on line 13
So I went through the process of deactivating other plugins and it activated fine. I then reactivated all others one by one and all good, until I tried to go to the Hummingbird dashboard, and just got a blank page. It appears to load fine IF the WPMU dashboard plugin is deactivated, but not activated.