BISM: value of the 'EffectiveUserName' XML for Analysis property is not valid

I've been working with Power View reports and one of the items I was setting up was using a BISM Data source connecting to an Analysis Services Instance in Tabular Mode. When I went to spin up a new Power View Report against the BISM Connection, I got the following error:

An error occurred while loading the model for the item or data source "http://sqldenali02/Reports/AW Internet Sales.bism". Verify that the connection information is correct and that you have permissions to access the data source.