I can not write a new message in the Windows Vista Deployment and Imaging forum as, when I have to choose, from the list, the forum on what to write, this forum does not exist. Why?
There are lots of threads here that talk about posting problems like that. Check the URL in the address bar of your browser. It has to start with social.technet.microsoft.com. You can see the forum from other URLs too, like social.microsoft.com, but you won't be able to post to the forum. Hans Passant.
There's another possibility that is much rarer but does exist.
You can be in the correct forum set (technet say) and the forum can be listed in the list of All Forums (for that technet set) but it still isn't listed in the forums you can post to.
The reason for that (in the case I am thinking of) is that the forum is read-only.
So it is NOT listed as a forum you can post to, but IS otherwise listed and the posts that are there can be read.