Are there any other settings, besides disabling "Check Out", to enable Co-Authoring in Excel? When I open Excel, all I get are the options in the image I attached. I do not get the "Edit" option that I'm looking for, even though I have Full Control in the library and the site in SharePoint 2010. btw, I have "SharePoint Server Enterprise Site Collection features" enabled as well.
The Excel 2010 client application does not support co-authoring workbooks in SharePoint Server 2010. However, the Excel client application does support non-real-time co-authoring workbooks stored locally or on network (UNC) paths by using the Shared Workbook feature. Co-authoring workbooks in SharePoint is supported by using the Microsoft Excel Web App, included with Office Web Apps. Office Web Apps is available to users through Windows Live and to business customers with Microsoft Office 2010 volume licensing and document management solutions based on Microsoft SharePoint 2010 Products. For more information, see Office Web Apps (Installed on SharePoint 2010 Products).
Do you have the office web apps installed?