WPMUDEV Dashboard update failing

We are running a large multisite which is sat behind a server running nginx acting as a load balancer to forward the public traffic to two servers running wordpress, they use rsync to synchronise the public_html folders. These are in turn linked to two mysql servers which are using mysql replication and connected to the wp servers by hyperdb.

When we click on the wpmudev updates and then select the dashboard plugin we get a pop up saying are you sure you want to do this and a link to try again which does nothing.

ANy ideas?