Error creating Web Sites Rule

I receive this error when attempting to create a rule that monitors the Average Response time of my Azure Web Site:

<string xmlns="http://schemas.microsoft.com/2003/10/Serialization/">{"Code":"BadRequest","Message":"Exception of type 'Microsoft.WindowsAzure.Management.Monitoring.Rest.MonitoringServiceException' was thrown."}</string>

In the Operations Logs this is the ID:
7312bdfe-ba79-4d65-9044-9c1e31367930

GS