[j-nsp] ScreenOS problem

[SunnyDay]

Hello
i have am ssg 140 running screenOS 6.1.0r2.0.
i have 2 adsl pims load balancing traffic.i have configured to adsl1/0
a dsl subinterface with a different pvc and different pppoe 
connection.The problem
is after 2 or 3 days the adsl interface is down and a restart is 
required for the interface to come up again.
Does anyone know if its maybe a bug or something else to look in the config?

Thank you.