Sftp does not work after upgrade fo F12

[Gianfranco Durin]

Dear all,
I have used for ages ssh and sftp with Fedora 10  on my machines, then I 
upgrade them receenty using preupgrade to Fedora 12.

SSH still works very well, but sftp fails with error "Could not 
initialize SFTP session". I get this in both directions, I mean when 
using sftp from one machine to the other and reverse.

The problem is that I have no idea on where I should look to understand 
the problem... could someone help me?

Many thanks
Gianfracno