Oops… there was a problem during the request after upgrade (no replies)

Just upgraded to the new beta 2.5 and now Piwik has stopped working properly. Firstly. I get "Oops… there was a problem during the request. Maybe the server had a temporary issue, or maybe you requested a report with too much data. Please try again. If this error occurs repeatedly please contact your Piwik administrator for assistance." when I click on any site and also from the dashboard, the evolution graph is showing a missing image.

Piwik has been working great for over 2 years but this new beta broke something.

Anyone know how to solve this?

Thanks

Jean