I know, that this topic is quite old, but I've found it looking for a solution for exactly the same problem. (V-USB current version)
Using attachInterrupt on pin 3 (as V-USB is configured for 2) triggers WInterrupts library to load. WInterrupts defines for whatever purposes INT0_vect and INT1_vect. But one of them was already defined by V-USB library (depends on which pin VUSB was configured: pin 2 - INT0 or pin 3 - INT1). So there is the collision.
Probably there is a possibility to modify WInterrupts or VUSB library. But it's dirty and I do not like to do things that way.
The solution was to not use WInterrupts library. Since attachInterrupt is just an easy way to setup interrupt, it has to be possible to set it by hand, the hard way. And it is!
So I just found some examples of configuring interrupt and make it for INT1. This page is extremely helpful. And my configuration (for FALLING):
// activate external interrupt 1
EICRA &= ~(bit(ISC10) | bit (ISC11)); // clear existing flags
EICRA |= (0<<ISC10)|(1<<ISC11);
EIFR = bit (INTF1); // clear flag for interrupt 1
EIMSK |= bit (INT1); // enable it
and of course:
ISR(INT1_vect) {
//do something on interrupt
}
And it is awesome now ^^.