In Excel 2013 when exporting data to Excel from Microsoft Dynamics CRM I get the error:
"The file format and extension of "FILENAME.xls" don't match. The file could be corrupted or unsafe. Unless you trust its source, don't open the file"
I got the same error when I had Excel 2010 but was able to find a registry key workaround that make the error go away. Now that I've upgraded to 2013 the error is back. The same registry keys don't look like they exist for 2013 and I've not been able to find anything online for a fix. Any advice?
Here is the fix for Office 2010:
Key:HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security
Value: (DWORD)"ExtensionHardening"
= [0 = Disable check; 1 = Enable check and prompt; 2 = Enable check, no prompt deny open]
Default setting if value not present is 1 (enable and prompt).