[mpls-linux-general] difficulties configuring f8+mpls: RTNETLINK answers: No such file or directory

[lucapilosu\@libero\.it <luc...@li...>]

Hello, finally I passed to fedora 8 on all the PCs of my testbed, but now I have a problem while configuring MPLS.
At the moment my testbed is as follows:

(pc A)------(LER 1)-----(LER 2)------(pc 2)

When I run the command
#mpls nhlfe add key 0 instruction push gen 1000 nexthop eth0 ipv4 10.0.2.4

The system answers the following:

RTNETLINK answers: No such file or directory

If I type 
#mpls nhlfe show

the output is
RTNETLINK answers: No such file or directory
Dump terminated.

I've read something about some QoS modules to be builded within the kernel, but I really don't understand what's the problem.
On the 2 LERs I've installed f8 xfce (other desktop environments were too heavy for my old pentium 3), then I added mpls.repo and I launched the package updater.
The only difference I noticed between this installation and other ones with f8KDE is that the new entry of the boot loader was 
Fedora (2.6.23.15-137.fc8.mpls.1.960)   ---on "KDE PCs"
and
Fedora (2.6.24.3-12.fc8)    ---on "XFCE PCs", but the command mpls is available!
Could it be the xfce distro is different from f8KDE?
Sorry if all my questions are not too clear, but really I don't understand what's my actual problem!!!
Thank you,
Luca