problem with ftp and apf

[j0sh]

hi all
i installed apf months ago... all was right untile some days ago

after a dist-upgrade i can't transfer backups via ftp from my server to others

if i connect via shell in ftp and try to transfer files on a remote server all i receive this error
421 Service not available, remote server has closed connection

but if i stop apf all is right...

someone had a similar problem?