"None" is always grammatically singular in English textbooks, but actual usage is variable, with many people feeling that it represents a group and therefore needs a plural agreement. In formal writing, I insist on students making agreement with the singular; in other contexts, either is fine.
True, but then why is "Uskyldig" plural? If "none of us" is the subject, and the subject is singular, then shouldn't the adjective agree with that as well?
I said "None of us are innocent" which, as pointed out, is not grammatically correct. It was, however, accepted. Since it's not correct it shouldn't be accepted.