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I have a web app that saves files as .xls but are actually well formatted .html. The files have always opened with excel producing the following warning:

The file you are trying to open 'file.xls', is in a different format than
specified by the file extension. Verify that the file is not corrupted 
and is from a trusted source before opening the file. Do you want to open
the file now?

Without warning the message has stopped appearing and the excel files open blank. Some users are able to open the files and see the data and others have the same experience with the blank page and no warning.

I have tried double clicking the file as well as opening the file from within excel. Neither option works.

I have not been able to find a solution.

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1 Answer 1

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Microsoft has released updates that have caused some downloaded files not to open, most notably HTML with .xls extension. The updates in question are:

  • Windows Update KB3115262 (Excel 2013)
  • Windows Update KB3115130 (Excel 2010)

I have found several options that can eliminate the problem.

Option 1

  • Control Panel > Internet Options
  • Security Tab > Trusted Sites
  • Add the site you are downloading from to the trusted site list

** You will need to re-download excel files once this change is made. Files previously downloaded when untrusted may still open blank **

Option 2

  • Go into the properties of the file you have saved to your computer (right click it, then left click properties)
  • Click Unblock
  • Click Apply
  • Open the file

Option 3

  • Open Excel Go to File Options
  • Click Trust Center -> Trust Center Settings
  • Go to Protected View. there are 3 options that show that were all clicked. Uncheck the first option that reads -- "Enable Protected View for files originating from the Internet"

Option 4

  • Open Excel Go to File Options
  • Click Trust Center -> Trust Center Settings
  • Go to File Block Settings
  • Uncheck Web Pages and Excel 2003 XML Spreadsheets

Option 5

  • Uninstall the previously mentioned update that applies to your Office version
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