Preventing black boxes around hyperlinks?

My document, created in Word 2010 and saved as a pdf in Adobe Acrobat X Pro 10 (newest version), has hyperlinks referring to other areas of the document.  The document looks fine on my screen (on a PC) and other screens, but on a particular computer (that happens to be a Mac desktop) it shows black rectangles around the hyperlinks when opened in Adobe Reader.

I went into the edit links dialog, and it shows the Link Type as Invisible Rectangle.

How to I prevent this from happening on certain computers?

Thanks!