I'd try re-downloading it again, just did a test with a fresh download on two different 2.3.4 boards and it seems to work just fine.
I've seen that error when people may extract then zip up again, or the file didn't finish downloading. Your zip does end in 2.3.4, correct? Also, do you have that TH Install and upgrade add-on by chance? I've seen issues with that plugin installed.