title: Why are EXCEL XLSM format no longer a valid ZIP format?
body: <p>Files saved in Excel as XLSM files are no longer valid ZIP files, preventing editing of the Ribbon. </p>
  
  <p>XLSM files saved on or prior to May 23, 2014, can be renamed .ZIP and edited.</p>
  
  <p>XLSM files saved after May 23, 2014, cannot be renamed .ZIP and edited, but rather generate the error message that the file is a corrupted archive. Both Windows Explorer and WinZip generate the same error condition, though the error message varies slightly.</p>
  
  <p>Yes, there are macros in the files; but even opening an old file with Macros (and VBA) disabled and immediately Saving As a new name generates a corrupted file.</p>
  
  <p>I have also tested on 2 other machines in our corporate group, with the same results, so it is not a corruption just on my workstation. </p>
  
  <p>Office Diagnostics reports no problems with EXCEL.</p>
  
  <p>Any thoughts on causes or solutions?</p>
  
  <p><strong>Update</strong></p>
  
  <p>Let's be clear on my test process:</p>
  
  <ol>
  <li>I rename an XLSM file saved on May 23 to .ZIP; this creates a zipped archive which both WinZip and Windows Explorer can open successfully. I then undo the rename to make the file an XLSM again.</li>
  <li>I open the file above in EXCEL-2007 <strong>and do not enable macros or VBA</strong>. I save this with a new filename as an XLSM file.</li>
  <li>I rename the file saved in step (2) as a .ZIP file. This file no longer opens in either WinZip or Windows Explorer, but generates the error message above.</li>
  <li>I repeat steps 1 through 3 above on the workstations of two other colleagues - same result exactly.</li>
  </ol>
  
  <p><strong>Update #2</strong><br>
  The problem seems to be file-related in some way, as saving an empty workbook as an XLSM still works. I will investigate more.</p>