@gcairns are you using Power BI Pro? or Free. See Keith's last comment, the issue went away with a Pro license. I don't recall reading that requirement anywhere, but it wouldn't surprise me as in the GA you need SQL Enterprise, and since you need a Pro license to use SQL as a datasource, since SSRS is a component of SQL - you need a PBI Pro license.
I'm getting the same error but I'm an admin on SSRS and the owner of multiple Power BI groups.
Also, I successfully congifured the Power BI integration and have SQL Server 2016 SP1 CU2.