Analog ports problem


I am using only GUI to configure my system. Each user has a diferent port. I don’t have dial tone on ports 17,19,21,23, but in the other ports 18,20,22,24 everything is OK.

System details:
RHEL 5.2
Asterisk last version
Digium AEX 2400 with 8 FXS and 8 FXO

Thanks for your assistance,