For my Rainbowduino i use the Frameware from Seeed (Google Code Archive - Long-term storage for Google Code Project Hosting.)
When i am flashing it to my Rainbowduino the very last line of my 8x8 RGB Matrix lights up and nothing else seems to happen..
I found out, that when i am removing line 73:
TIMSK2 |= (1<<TOIE2);// | (0<<OCIE2B); //Timer2 Overflow Interrupt Enable
The last line does not light up anymore.