AVR-Chat

I am using winavr 3.4.1 with AVR studio 4.1.

I am trying to find out why my code is no longer driving my motors.
Anyhow I am stepping through it in AVR Studio and every so often I get
jumped to the default interrupt vector. I have defined a default
interrupt routing that just return.  (I did this because otherwise it
would just reset the MCU.) I think this may be related to my problem.

I have the following interrupts defined

SIGNAL(__vector_default)
SIGNAL(SIG_INTERRUPT6)
SIGNAL(SIG_INTERRUPT5)
SIGNAL(SIG_OUTPUT_COMPARE0)
SIGNAL(SIG_INPUT_CAPTURE3)
SIGNAL(SIG_UART0_RECV)
SIGNAL(SIG_UART1_RECV)
SIGNAL(SIG_UART0_TRANS)
SIGNAL(SIG_UART1_TRANS)


In the I/O panel the following items are in red (meaning changed on the
last single step
TCNT3L
ETIFR (OCF3A, OCF3B,OCF3C are set) (listed under Timercounter3)
ETIFR (none are set) (listed under Timercounter1) 

This would suggest something related to timer3
Here is my relavant code for timer 3

TCCR3A = BV(WGM31) | BV(WGM30); /* set timer/counter 3 to PWM mode 3 */
TCCR3A |= BV(COM3A1) | BV(COM3B1); /* Clear OCnA/OCnB/OCnC on compare
match when up-counting. Set OCnA/OCnB/OCnC on compare match when
downcounting.*/
TCCR3B |= BV(CS30) ; /* prescale: 1 @ 16 MHz, 10 bit PWM overflows @
15625 Hz giving 7812 HZ */ 
ETIMSK |= BV(TOIE3); // enable overflow interupt so we can set pwm in
int routine


Does anyone see anything wrong?