Hi,
1) What's the width of the pulses? Not the time between them but the width?
2) What's the value stamped on your x-tal?
3) The timing calculations that I provided are based on the fact that your chip is SUPPOSED to run at 40MHz, if it's not running at 40MHz then the timing will be wrong and the interrupt frequency will wrong as well.
4) Please don't quote the complete message you're responding to. It clutters the thread and it gets hard read because everything is quoted all the time - that's my personal view.