DTOO292 - Excel - Document behavior if file validation fails must be set - OpenInProtectedView
This policy key controls the behavior of how Office documents should be handled when failing File Validation. The options available are: -Block files completely. This will prevent users from opening files. -Open files in Protected View and disallow edit. This will prevent users from editing the files. -Open files in Protected view and allow edit. This will allow users to edit the files. If disabling or not configuring this policy setting, the default setting will be, 'open files in protected view and allow edit'.
Set the policy value for User Configuration -> Administrative Templates -> Microsoft Excel 2010 -> Excel Options -> Security -> Trust Center -> Protected View 'Set document behavior if file validation fails' to 'Enabled: Open in Protected View' and Unchecked for 'Do not allow edit'.