You need to look at the logs on the server as described here Upgrading from 2.9.0.beta8 broke the site, unrecoverable - #11 by Benjamin_D
That topic describes a similar problem which may or may not be related to adding the plugin.
You need to look at the logs on the server as described here Upgrading from 2.9.0.beta8 broke the site, unrecoverable - #11 by Benjamin_D
That topic describes a similar problem which may or may not be related to adding the plugin.