Touchpoint API Help

I am trying to write a silo launch program with wireless redstone, ICBM and CC and when I try to run my program it comes up with the error message: touchpoint:151:attempt to call nil.

Line 151 in the touchpoint api is:

local x, y = buttonInstance.mon.getSize()

So what is the problem? I don't understand it and I am bad at lua so any help is appreciated.

Thanks.

Could you post the code you're using, please?

It looks like you are having a problem with the monitor. Complete code would be helpful, if it is short put it in some Code tags if it is longer upload it to pastebin.