hi, ok i had this problem along with another problem which i managed to fix,
basicly the POP3 error is caused by two POP3 servers running on your box,
CPanel uses its own POP3 server called CPPOP and some linux OS's have a POP3 server in xinetd.d so you have to disabled that.
to do so heres a step-by-step using SSH as root
Code:
cd /etc/xinetd.d
vi popa3d
press 'i' to enter edit mode
change the line:
to
down press esc twice, then press ':' followed by wq then press enter
now do the same with popa3ds
vi popa3ds
finerly login to your WHM and restart your POP3 service
hope this helps,
Philly