Arithmetic Error in Turtle Program

So I've been working on a system that works like this.

tell computer which food you want
computer tells turtle to retrieve item from chest via rednet
turtle drops item into enderchest

All but one part is working; The turtle either doesn't stop when it supposed to, or, if I alter the code slightly; it moves one block and prints this error; "Attempt to perform arithmetic __sub on number and nil"

I'm still figuring how to put up my codes, so I'll just create this post for now and add the code in a bit.

Thanks for your help.

Ok so I can't figure out how to show you guys my code, any help with that?

Thanks again

Split into new topic.

Copy and paste the code into your post or upload it to pastebin and link to it here.