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.

Projects/XPLAINBridge/XPLAINBridge.c

@@ -81,6 +81,7 @@ int main(void)
 	Buffer_Initialize(&UARTtoUSB_Buffer);
 
 	LEDs_SetAllLEDs(LEDMASK_USB_NOTREADY);
+	sei();
 
 	for (;;)
 	{

Projects/XPLAINBridge/XPLAINBridge.h

@@ -40,6 +40,7 @@
 		#include <avr/io.h>
 		#include <avr/wdt.h>
 		#include <avr/power.h>
+		#include <avr/interrupt.h>
 
 		#include "AVRISPDescriptors.h"
 		#include "USARTDescriptors.h"