Sharepoint and PowerPivot: Connections fail to refresh in SQL Server 2008 Denali CTP3

Sharepoint requires a range of troubleshooting skills because it can involve the integration of various applications, which are necessarily resting on the application stack. I have the deepest respect for SharePoint specialists since i know that the troubleshooting skills can cut across applications and an understanding of the 'glue' that welds SharePoint together. Take, for example, the issue which I found recently whilst importing a PowerPivot into SharePoint. Everything looked absolutely fine: the PowerPivot loaded nicely into the PowerPivot gallery, and I could see my Excel spreadsheets too. The black and lime-green SharePoint theme was carried on throughout the Excel workbooks, and the whole thing was looking great. The Excel slicers were highly customised to match the SharePoint theming and customer branding, and the whole pieces, put together, looked fresh.