Null pointer exception fatal error in PP model deployed to SP2013

Question

I have a PowerPivot solution built in Excel 2013, which I have deployed to a SharePoint 2013 single server farm, which is also running SSIS/SSRS/SSAS 2014. 
I have configured data refresh jobs, which are running successfully, according to the PP management dashboard in SP.
I attempted to open the file from the document store in SP directly, and when I went to make modifications to the data model, tom horror I was greeted with "We couldn't load the data model. This may be because the Data Model in this workbook is damaged".
Further clicks on the OK button provide a bit more context.
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Error Message:
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Object reference not set to an instance of an object.
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Call Stack:
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at Microsoft.Office.PowerPivot.ExcelAddIn.InProcServer.CannotUpgrade(GeminiWorkbook geminiWb, WorkbookConnectionwbConn, String& message)
at Microsoft.Office.PowerPivot.ExcelAddIn.InProcServer.LoadSandboxAfterConnection(String errorCache)
at Microsoft.Office.PowerPivot.ExcelAddIn.InProcServer.LoadSafeSandboxAfterConnection(String errorCache)
at Microsoft.Office.PowerPivot.ExcelAddIn.InProcServer.LoadOLEDBConnection(Boolean raiseCompleteEvent, String errorCache)
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Unfortunately I've seen this before, and unfortunately it's been fatal. Fortunately since the last time I've seen this, I've become a bit more adventurous. Here's what I've done, and I'd really appreciate some community help to take this the last few inches
to a conclusion. Maybe some help from the Office team, since you're 15 minutes from my office :)
Using Visual Studio, I can see that the data model itself is intact. I was able to start a new solution using the supposed corrupt file as a starting point.
That's a good thing, but I don't know how to recycle it into a new Excel file so I don't lose all of the work I've put into it.
Using SQL Management Studio, using SELECT * FROM [PowerPivotServiceApplication1_endpoint].[dbo].[Versions] I can see that the reported Version is 12.0.1.0.
Also using SQL Management Studio, I can see that the server version for the server used for PowerPivot is 12.0.2000. I wonder if this version disparity is causing Excel to want to upgrade my file, and this is triggering a larger issue?
I seem to recall seeing somewhere that PP for SP2010 was not supported in a single server farm. I don't know if the same is true for SP2013, and frankly don't care (at this point, since all I am after right now is my data model back). I'm wondering if the
SP data refresh jobs are causing this, and the null exception is maybe a pointer to a second server in the "farm" that doesn't exist.
Lastly, I am more than willing to make changes to the underlying XML files that make up the XLSX file. If there's a way to know where the null value is being referenced (if possible) and make it go away, that would be stellar. 
Any help is greatly appreciated. Like I said, I'm very willing to go down deep rabbit holes, sit with devs, whatever it takes.
Thanks 
Any help on this is greatly appreciated. I'm 

Answer 1

Here's one thought...
Because the error occurs with more workbooks, the reason is probably external to the files, model etc. but common to it,
such as permissions or user specific policies on his workstation or servers involved, This Microsoft Excel Support Team Blog article is an example of a cause for a similar seemingly scary error message:
http://blogs.technet.com/b/the_microsoft_excel_support_team_blog/archive/2013/08/27/powerpivot-for-excel-2013-error-when-opening-the-manage-window-quot-we-couldn-t-load-the-data-model-this-may-be-because-the-data-model-in-this-workgroup-is-damaged-quot.aspx 
Ed Price, Azure & Power BI Customer Program Manager (Blog,
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