title: Turning off Excel Compatibility Checker for "Significant Loss of Functionality" errors
body: <p>I've found that, while it's possible to programatically disable Excel's "Compatibility Checker" via code (by using <code>ActiveWorkbook.CheckCompatibility = False</code>, either before a <code>SaveAs</code> call or globally by trapping the <code>ActiveWorkbook.BeforeSave</code> event), it doesn't seem to work if there is a "Significant loss of functionality" detected. Quick way to test this:</p>
  
  <ul>
  <li>Create a new Excel 2010 workbook.</li>
  <li>Select A1:A2 and choose a conditional formatting (doesn't matter what).</li>
  <li>Select A2:A3 and choose a different conditional formatting. A2 should have two different conditional formats applied.</li>
  <li><p>Open the VBA editor, and add the following code to the Workbook module:</p>
  
  <pre><code>Private Sub Workbook_BeforeSave(ByVal SaveAsUI As Boolean, Cancel As Boolean)
      ActiveWorkbook.CheckCompatibility = False
  End Sub
  </code></pre></li>
  <li><p>Put a breakpoint in the code.</p></li>
  <li>Back in the spreadsheet, select File > Save As. The code will immediately jump to the breakpoint. If you step through the code, you can verify the <code>CheckCompatibility</code> setting in the Immediate pane.</li>
  <li>Once the code has completed, choose the Excel 97-2003 file type and click "Save."</li>
  <li><strong>The compatibility checker still comes up.</strong></li>
  </ul>
  
  <p>I suspect this is because the error isn't a "minor compatibility issue" (cf. <a href="http://msdn.microsoft.com/en-us/library/office/gg132972(v=office.14).aspx" rel="nofollow">http://msdn.microsoft.com/en-us/library/office/gg132972(v=office.14).aspx</a>) but nothing I do seems to suppress this error, not even creating a registry entry to disable it. Anyone have any idea how to suppress the checker even with "significant" incompatibility?</p>
  
  <p>ETA: Without going into a lot of unnecessary detail, I'm trying to automate a process where a number of vendor templates are opened, populated with data, processed according to an enormous (and always slightly different) set of quality control rules, and saved back out as an .xls file (per the vendor's requirements). Because this happens on dozens of different template workbooks every two hours on an unattended system, I can't simply uncheck the compatibility requirement on a per-workbook basis. I mean, I suppose I could, but that would become my full-time job. I need to be able to turn off compatibility checking at run-time for any workbook, the first time, without human intervention.</p>