Is night service on? By default, the nightime dial 0/timeout is transfer to the gen mbox.
To chek the day:
ICM 777
mbox 0 #
Pswd: 123456 (may be different)
Press 9
option 3 for AA
enter AA number (probably 1)
Press 6 to modify.
press 0 for the dial 0 timeout action.
If you make a change you will need to press *# after the change. Then when it asks if you want to re-record a new menu prompt, just press #.