It sounds like the PRI card may be intermittenly failing . The only sure way to tell is to stat the plid when this trouble occurs . From the maint screen you would type lets say STAT 7 1 1 1 you would then see the condition of all 23 channels . They should all list back as being IDLE or BUSY . If some or all list back as either OUT OF SERVIVE, NOT SEIZEABLE , MANBUSY . Then change back to IDLE or BUSY without any intervention you most likely have a faulty PRI card . You may also want to check your clocking stats and clocking source . When I have a chance I will Private Message you with how to check your IMAT version . Thanks

Let It Be , I live in a Yellow Submarine . SCCE