The near_redshift and far_redshift are free parameters for you to set, and just control the redshift interval over which to make the light cone projection. You might also want to look at the narrative documentation on the light cone generator, which you can find here:
Note, that you need to use this with a simulation that made enough data outputs to connect the redshift interval you specify. The "enzo_tiny_cosmology" dataset available at http://yt-project.org/data/
was configured to work with the light cone recipe in the cookbook, so I would suggest downloading that.
As for the error, this is happening because there is a line in your enzo parameter file that contains more than one "=" sign. I have just submitted a pull request that fixes it, so this should be fixed soon. In the mean time, you can simply comment out that line in your parameter file and everything should work fine.