That error from what I can tell might refer to server space (as one part). But doing a Google search, a lot of people experience this. I did a search in Google with this:
wordpress PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature
But this WordPress thread you may want to check out: http://wordpress.org/support/topic/incompatible-archive-pclzip_err_bad_format-10
I can agree that the parent/child thing can be confusing… basically these are two separate themes, but how it works that the child theme connects to the styles and functions of the parent theme and duplicates the parent theme. Because these are separate themes, when you update the parent theme, the child theme will adopt the new changes, but whatever was changed with the child theme, these won’t get overwritten because again, it’s a separate theme (separate files). Still a bit confusing but it’s why WordPress recommends any core changes to the theme is best done with the child one.