It almost certainly means you have an (unintentional?) recursion in your code (a function that calls itself, which calls itself, etc...):
def recurse recurse recurse
Every time a function is called, a new frame is added on the stack. At some point, the Ruby interpreter decides that you have way too many stack frames and throws that error.
If you want to post the offending piece of code, we might be able to help with more specifics.
Max