Logging in to Fedora 15 does not automatically acquire AFS tokens. You can use the pam_afs_session module to get access to AFS automatically during console login or ssh access.
yum -y install pam_afs_session
echo "session required pam_afs_session.so always_aklog" >> /etc/pam.d/system-auth
echo "session required pam_afs_session.so always_aklog" >> /etc/pam.d/password-auth
If you are still having problems, add 'debug' to the end of the two lines provided above and check /var/log/secure to see what the session module is doing.