Seriously? The message tells you to make sure you have the latest version, but instead of doing that you make a thread?
Any way...exactly as the message insist....you have an outdated version of redsn0w. Only the current version supports iOS 5.1.
You need redsn0w 0.9.10b6. That is the only version that can jailbreak iOS 5.1.
I also recommend that you actually do some research on the difference between a tethered and untethered jailbreak.
The jailbreak for iOS 5.1 is a "tethered" jailbreak.
Don't bother asking when the untether comes out....no one will ever be able to answer...not even the devs themselves. It will be a while...hopefully month.