That’s a typekit font. Be sure to enable it in your preferences.
Thank you for the reply Bob, I should have included that this is the standalone version of CS6 not the CC subscription version. I tried to fine out how to enable typekit fonts but I don't believe this was purchased as a typekit font and if it was all I have are the font files in a .zip file. How would I enable typekit fonts in the standalone CS6 InDesign?
Typekit is not included with perpetual licensed products.
A script could make short work of replacing Museo Sans to Museo Sans 500. Without a script you'll have to do this manually in each file using Type > Find Font.