How do I get past the other guard on the second floor

Have you talked to the drunken guard yet?

And found out the commanding officer's name?

If not, you need to talk to the drunk until he reveals it to you.

Now, tell the guard (in the grey uniform):

* You're on official business.

* He should remember you.

* He shouldn't speak that way to a superior.

* Colonel Vogel knows you.