Getting error Input string was not in a correct format.

I have a problem with a String not in correct Format error.  My program was working perfectly
but something must have been changed because now I am getting this error. 
My program consists of a Button to enter two random numbers, and a check whether these
numbers are 7, 2, 12 or some other.  If the numbers add up to some other number I have a
Button with code that checks whether two new random numbers add up to the ones from the
first Button click.  In other words I am doing a dice game.  The problem is confusing because
sometimes when I click on the first Button I get an error message and sometimes not.  At 
times it will go through to the Button2 and after I click this Button it will give me an error
message.  I also have a user enter ...