why do I get 3072 error code when trying to download 6.0.4

Some details, please?

Based on the version number, you seeking to upgrade Safari?

What OS X version?

How are you upgraded or downloading the software? (Directly downloaded, or via Software Update?)

Have you tried quitting all applications, and then performing the Software Update? (Discussion per this thread — but that thread is for iTunes, and I'm guessing you're looking at Safari here?) If that doesn't work, I'd keep everything quit, reboot, and try again.