I tried the commands you gave, and this time it crashed again:
NCP>set circ ewa-0 service enabled
NCP>set circ ewa-0 state off
NCP>
%%%%%%%%%%% OPCOM 15-SEP-2011 11:39:48.02 %%%%%%%%%%%
Message from user DECNET on SLAVE
DECnet event 4.7, circuit down, circuit fault
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