Child theme Twenty Elven

Hello

I am in a very big trouble, I didn’t know about the need to have a Child theme. So I had started to modify the original twenty eleven theme, and then when I’ve realized that I need I child theme I created one from the modify-twenty eleven, and now when I want to edit the style CSS, this give me an error, which says something like that: ” This theme is broken. We found the main theme. Please install the theme “Twenty Eleven”.

Sorry for my bad English,

I hope someone understands my problem and can help me.

Thank you