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.

Bootloaders/CDC/BootloaderCDC.c

@@ -69,6 +69,9 @@ int main(void)
 	/* Setup hardware required for the bootloader */
 	SetupHardware();
 
+	/* Enable global interrupts so that the USB stack can function */
+	sei();
+
 	while (RunBootloader)
 	{
 		CDC_Task();

Bootloaders/CDC/BootloaderCDC.h

@@ -42,6 +42,7 @@
 		#include <avr/boot.h>
 		#include <avr/eeprom.h>
 		#include <avr/power.h>
+		#include <avr/interrupt.h>
 		#include <stdbool.h>
 
 		#include "Descriptors.h"