The glibc-2.3.6-3 was the guilty, after downgrading to 2.3.5-10.3. the yum working again.
Monday (27. march) I upgraded with Yumex the programs what where signed with +. Unfortunately I not remember which programs where these ones.
After reboot Yumex/Yum cannot to find any repo site. Repo files are unchanged in my FC4.