where you translated "string" into "cadena".
This is not allowed, these lines have to be left untranslated.
Similar is with
"#d-i netcfg/dhcp_options select Configurar red manualmente\n"
This line has be left as:
"#d-i netcfg/dhcp_options select Configure network manually\n"
And additionally, I corrected some over-long lines (change line breaks), because otherwise those long lines look ugly in the PDF variant of the
manual (so only a cosmetic changing, nothing strictly wrong from you side).