Blackscreen (java.io.FileNotFoundException) (Seems to be a login bug)

When I launch MC with normal launcher is blackscreens. With dev laucher (1.5.2) it also does this. This is the error:

Client> java.io.FileNotFoundException: http://assets.minecraft.net/1_6_has_been_released.flag
Client> at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
Client> at kn.a(SourceFile:234)
Client> at bkg.run(SourceFile:113)
Client> at java.lang.Thread.run(Unknown Source)

This is only for 1.5.2 and launchers where you have to log in. 13w22a works. My cracked launcher (no login required) also works. Playing from minecraft.net works.

How to recreate: Launch 1.5.2 with dev launcher.

Fix this ASAP please.

Thanks