WPA-PSK Group Policy: No field to enter the PSK

Hi,

im trying to set up a Group Policy (Windows Server 2003 SP1) to configure
the Wireless LAN settings. If I choose the Network Authentication WPA-PSK
there is no field where I can enter my Pre-Shared-Key (it doesn't matter
which Data encryption option I select). The field "The Key is provided
automatically" is checked and greyed-out, so that I can't uncheck this field.
Does somebody know, where I can enter the PSK, or is this a bug?
I know that WPA-PSK is not intented to use for bigger environments, but for
my scenario it's ok.

Thanks in advance for your answers,

Denis Holtkamp