While deploying Monitoring Server, I was having trouble viewing dashboards from SharePoint, but preview was working fine. I referenced Nick and Adrian’s book and it suggested using the same identity for the SharePoint application pool for the credentials for the Monitoring Server application pool. I’m working in an environment where the SharePoint service accounts are already deployed and Monitoring Server is coming in later. The account names already in use for the SharePoint application pool wouldn’t make sense.
On page 241 on Nick and Adrian’s book, there is an awesome diagram of data/security flow for rendering a dashboard. (Buy the book – it’s great!)
Just don’t forget that for a preview of the dashboard, it will use the application pool identity of the Monitoring Server, but when you render on SharePoint, it will use the credentials of the application pool for SharePoint. If they are two different accounts, you’ll need to add them both with read permission to your data sources.
If you care to look and you are using SQL Server or Analysis Server as your data source, fire up Profiler and watch. You’ll see two different accounts.