title: Getting System Error &H80070057 (-2147024809)
body: <p>I've been running a workbook with a few macros in it for a couple of years, and I've suddenly started getting this error thrown at me for some navigational buttons (shapes linked to macros that are simply <code>ThisWorkbook.Sheets(&quot;sheet_name&quot;).Activate</code>).</p>
  <p>Other Macros within the workbook seem to work OK, but I can't get into the VBA editor to see any of the code anymore - I get to the VBA interface, but when I go to open the Module, nothing happens.</p>
  <p>And to cap it all off, when I try to save the workbook, I'm just getting an error saying 'Document not saved'.</p>