Problems with Atmega644P I2C together with timer1 and timer2

I am using an Atmega644P with arduino bootloader. I have an application with I2C and also timers 1 and 2. Timer2 is used to generate PWM and timer 1 generates an interrupt loop. Using a simple application without the timers i can talk to an I2C slave device using the normal Wire library. When the timers are active the system locks. Obviously something is clashing. Interupts ? timers ?. Does anyone have any experience with this and how can it be overcome. Which timers and which interupts does I2C use and can they be changed or my program timers changed.

thanks for your help


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