Hi first time posting, I figured out how to fix this after reading your posts above and this here
http://support.microsoft.com/kb/296492
TLDR see below for solution if you get the x' was an undeclared namespace problem that I did
1) Download notepad++ so you can edit your XML file easier, you can also choose to use regular notepad
2) For the noobs out there like me when I started this process - unpack the xlsx file by changing .xlsx extension to .zip, then unzip the zip to a folder since you can't edit files inside the zip folder (you will rezip later)
3) Open up the styles.xml file inside the xl folder using notepad++
3) Control find for "x:" to find instances where x is used as namespace
In my case, I found this:
<x:ext uri="{9260A510-F301-46a8-8635-F512D64BE5F5}" xmlns:x15="http://schemas.microsoft.com/office/spreadsheetml/2010/11/main"> defaultTimelineStyle="TimeSlicerStyleLight1"/></x:ext>
Since there is an x15 after xmlns: I know the name space here should be x15 and not x (according to the microsoft.com link at the beginning of this post)
So the <x:ext... should be change to <x15:ext... and the </x:ext> should be changed to </x15:ext>
4) Make these changes to all instances of x: to the correct namespace and hit save on styles.xml
5) Rezip the excel folder and change .zip to .xlsx
6) Open the file in excel - this worked for me but no guarantee it would work for you
Message me if you have any questions - thanks for the clues
http://support.microsoft.com/kb/296492
TLDR see below for solution if you get the x' was an undeclared namespace problem that I did
1) Download notepad++ so you can edit your XML file easier, you can also choose to use regular notepad
2) For the noobs out there like me when I started this process - unpack the xlsx file by changing .xlsx extension to .zip, then unzip the zip to a folder since you can't edit files inside the zip folder (you will rezip later)
3) Open up the styles.xml file inside the xl folder using notepad++
3) Control find for "x:" to find instances where x is used as namespace
In my case, I found this:
<x:ext uri="{9260A510-F301-46a8-8635-F512D64BE5F5}" xmlns:x15="http://schemas.microsoft.com/office/spreadsheetml/2010/11/main">
Since there is an x15 after xmlns: I know the name space here should be x15 and not x (according to the microsoft.com link at the beginning of this post)
So the <x:ext... should be change to <x15:ext... and the </x:ext> should be changed to </x15:ext>
4) Make these changes to all instances of x: to the correct namespace and hit save on styles.xml
5) Rezip the excel folder and change .zip to .xlsx
6) Open the file in excel - this worked for me but no guarantee it would work for you
Message me if you have any questions - thanks for the clues