Error with Sparkfun MP3 Shield and Arduino Due playing music files
The library is written for the Uno, not the Due. It relies on two instructions that are only available in the AVR compiler.

Newer versions of the core provide a pair of macros, interrupts() and noInterrupts() that should be used in place of sei() and cli() respectively, which should be provided by the Due's core as well to make it cross-platform. However that library has never been updated to work with those macros. 

You could replace the sei() and cli() calls in the library with interrupts() and noInterrupts(), however that may not make it work, since it was written with the Uno and other AVR based chips in mind.