USB_Init() no longer calls sei() to enable global interrupts - this must now be done in the user application once all init code has run.

Demos/Device/ClassDriver/MassStorageKeyboard/MassStorageKeyboard.c

@@ -89,6 +89,7 @@ int main(void)
 	SetupHardware();
 
 	LEDs_SetAllLEDs(LEDMASK_USB_NOTREADY);
+	sei();
 
 	for (;;)
 	{

Demos/Device/ClassDriver/MassStorageKeyboard/MassStorageKeyboard.h

@@ -42,6 +42,7 @@
 		#include <avr/wdt.h>
 		#include <avr/power.h>
 		#include <avr/interrupt.h>
+		#include <avr/interrupt.h>
 		#include <stdbool.h>
 		#include <string.h>