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Perhaps it is not Dynamics CRM - Updates to Excel

Dynamics CRM is such an integrated platform, it leverages a ton of really cool Microsoft Technologies and taps into the Microsoft technology stack. This means that you get all the power of Excel, Outlook, Word, SQL Server, Windows Server, Exchange and more!

Sometimes however an issue is not a CRM issue and is resolved with a service pack to one of the other applications. Take for instance Excel.

Check out this little Tidbit from the Microsoft Excel Support Team Blog.

Dynamics CRM files do not open in Excel 2013 as expected