You are unable to access any of the standard reports via the AMS dashboard.
You are getting GetGuid Error - Network Error and the main Oasis Portal randomly is showing HTTP Error 503. The service is unavailable.
In such cases please contact our Support Team to have the underlying issue solved.
This issue occurs when CRMAppPool and Microsoft Dynamics Unzip Service are not running on the IWS servers (eg: uk-o11-iws2) or when the Ad Hoc Reporting Servers are not running (eg: uk-o11-ahr1).
Restarting the given machine should solve the issue. See Volt Delta UK Server Information for the list of servers used for these roles.
Once our Support Team confirms that the underlying issue has been solved, the standard reports should open correctly.