I upgraded to kde 4.6 and i'd like to use the fish protocol as usually but it does nt work. Unknown protocol.
Is ther an option that i have to activate to have the fish protocol enabled again ?

You likely need to install the appropriate package. The fish protocol support is located in kde-runtime however, and thus should be installed and available (ie. your distribution's packages are defective if it is missing)

It works now without any modification
Maybe was a temporarly server side problem and was a coincidence the same time that i installed the 4.6