How to resolve connection errors when loading data in SSAS Tabular project

This post actually applies to both multidimensional (cube) projects and Tabular projects which manage data source connectivity in a similar fashion. The multidimensional design experience is different but the mechanics of the SSAS engine are essentially the same. When loading data from a SQL Server data source into a Tabular model project, chances are very good that you'll see an error on the first attempt. I've been creating SSAS projects for over over 15 years and, even though this is a relatively simple process, I still usually work through the initial configuration in trial-and-error mode. So, let's call this a normal part of the process.