Error - ERR POP EOF or I/O Error

Hi,

After upgrade my server to a HP Proliant 320L run Fedora 5 and Qpopper 4.09 
or Qpopper 4.08 and clients run Outlook 2000 ad 2003 and Symantec Corporate 
2006, many (no all) users receive error on "get mail".

In maillog write this error:
Aug  7 15:42:34 mail-srv02 popper[5368]: user at 192.168.2.110 
(192.168.2.110): -ERR POP EOF or I/O Error

I configure my Qpopper with :
./configure --enable-shy --enable-specialauth --mandir=/usr/man
or
./configure --enable-shy --enable-specialauth --mandir=/usr/man  --disable-old-spool-loc
or
./configure --disable-old-spool-loc --enable-shy --enable-specialauth --mandir=/usr/man 
 --enable-spool-dir=/var/spool/mail --enable-temp-drop-dir=/var/spool/mail.drop 
 --enable-cache-dir=/var/spool/mail.cache

My basic configuration run Qpopper on Xinetd with flags -s -R -S

Obs. if. disable Symantec 2006 on clients i can receive mail, but this 
antivirus using old server run no problem.

Any sugestions ??

Thanks