SCCM and remote desktop

HI,
i would like to know why, even if i enter as administrator, i cant change
the setting on a server with sccm.
Up to 2 days ago i was able to connect to the server from a xp machine.
Today, i tryed again and i got an error message.
Since i already know how to solve the problem related to that error message,
i will write the solution instead of the error:
to solve the problem you must go to the remote desktop setting and change
the remote setting from NLA to "allow connection from computer running any
version of remote desktop.

I know what you are thinking: "Why this guy post the question if he already
has the solution?"
Simple: Because they are all geryed out. I cant change anything there even
if my account is in the group administrators of the machine.

I think it could me a sccm setting. But where can i check it?

Thanks in advance for all the answers and sorry for my english

Regards,
Giovanni