ExecuteMso was added to Office 2010, but VBA in Office 2011 is more likely to be based on Office 2007. Therefore, you'll need to use only the methods available in Office 2007 & earlier. Not being a PowerPoint specialist, though, I can't advise on that.
I'll move the thread to the PowerPoint forum in the hope someone there will have an answer.
PS: See also
http://www.mrexcel.com/forum/general...-2010-a-2.html