Consider the following scenario: You have a SharePoint 2010 document library. You have Office Web Apps 2010 installed. On a SharePoint 2010 document library that contains Excel workbooks, the user can choose to 'edit in browser' or 'view in browser'. You open an Excel workbook that contains a circular reference, you are presented with no warning of the possible cause of it failing to render in the browser. There is no error message or warning of the file containing a circular reference.
This feature is not available in Excel Web Apps 2010 or Excel Services in Microsoft SharePoint Server 2010. For advanced error handling, utilize the Excel full client.
Differences between using a workbook in the browser and in Excel http://office.microsoft.com/en-us/web-apps-help/differences-between-using-a-workbook-in-the-browser-and-in-excel-HA010369179.aspx
How to remove or allow a circular reference (for Microsoft Office Excel 2007) ttp://office.microsoft.com/en-us/help/remove-or-allow-a-circular-reference-HP010066243.aspx
Excel web apps; circular reference