On upgrade to version 4, the existing IIS website for the Event Broker application failed to open due to a permissions error. This was subsequently resolved by re-enabling Integrated Authentication on the IIS website.
One possibility for the issue might be that the IIS application pool identity (svcFIM_EBrokerWeb) in this case is not configured to be the same identity as the Event Broker service account (svcFIM_EBroker - as specified in the MSI). However this is only a guess.
Customer support service by UserEcho