# What is the meaning of string index out of range?

I am dealing with [35,6] linear code over finite filed with 2 elements. I am able to get an output of its generator matrix as 6x35 matrix, but while computing parity check matrix which will be of size 29x35, I am getting following output: IndexError:string index out of range

Does it mean that its size is two large? If still it is so, how to get that matrix in sage??

Could you please provide the full code that lead to the error ?