Name resolution

[Eric Tanguy]

Since few days now i have a name resolution problem. For example when i 
entrer a new address in firefox it returns that the name can't be 
resolved. Reloading the page and firefox display fine the page. I have 
the same problem from thunderbird or cli using yum.
The network is up using network manager with ethernet and dhcp. The name 
server is the box ip. This configuration is the same as other pc on the 
same network and these pc don't have any problem so i think the problem 
is specific to this f15 machine but i don't how to investigate.
Any help ?
Thanks
Eric