Excel Services delegation

I am inspired by a recent post from a colleague about the various issues that can come up with Excel Services delegation (see a Denny Lee’s blog here:http://dennyglee.com/2009/11/18/troubleshooting-powerpivot-excel-services-connectivity/) and I wanted to take it a bit further (and maybe a bit ‘geekie’-er)

First, why is this a problem? After all, as you can see in Denny’s post, you can see the workbook and you even have a thumbnail for it in the Gallery. What’s up here? The core of the problem is that unless you’ve set the connection to refresh when you first open the workbook, Excel Services uses its pivot cache to construct the pivot table and slicers. It is only if you manually refresh the connection, or click on a slicer, that you make an actual connection to the embedded data. Until then you are just looking at cached information. Until you click on a slicer, you don’t really know if Excel Services is working – so a strong recommendation that I make to any person doing a validating their installation is to “ALWAYS CLICK ON A SLICER” if you want to make sure that your installation is working properly.

Ok, so now we’ve hit the problem. And you get the dredged “An error occurred during an attempt to establish a connection to the external data source.