You have Office Web Apps in your farm, and it can open all office document in browser, except for Excel.
- ULS logs shows following exceptions “ServerSession.ProcessWebException: A Web exception during ExecuteWebMethod has occurred for server: http:/../exc/ExcelService*.asmx”
- Restarting Excel calculation services doesn’t help
- Reconfigure connection OWA server to SharePoint doesn’t help
- You have Microsoft Monitoring Agent tools installed in OWA server
- Uninstall Microsoft Monitoring Agent from OWA server