Asterisk restart

Hi all, i’ve a strange problem with my pbx…
I noticed that sometimes, when i’m conneting to pbx console, the connection drops, the calls are ending and all restart…
I think that Asterisk crash and restart itself…
Watching the full log i see

Jul 24 17:59:58 WARNING[5411] channel.c: Thread -1225770064 Blocking ‘mISDN/8-1’, a
lready blocked by thread -1239561296 in procedure ast_waitfor_nandfds
Jul 24 17:59:58 WARNING[5411] channel.c: Thread -1225770064 Blocking ‘mISDN/8-1’, a
lready blocked by thread -1239561296 in procedure ast_waitfor_nandfds
Jul 24 17:59:58 WARNING[5411] channel.c: Thread -1225770064 Blocking ‘mISDN/8-1’, a
lready blocked by thread -1239561296 in procedure ast_waitfor_nandfds
Jul 24 17:59:58 WARNING[5411] channel.c: Thread -1225770064 Blocking ‘mISDN/8-1’, a
lready blocked by thread -1239561296 in procedure ast_waitfor_nandfds
Jul 24 17:59:58 WARNING[5411] channel.c: Thread -1225770064 Blocking ‘mISDN/8-1’, a
lready blocked by thread -1239561296 in procedure ast_waitfor_nandfds

i’ve cut many lines…(40/50) and then * restart

Jul 24 18:00:02 VERBOSE[20390] logger.c: Asterisk Event Logger Started /var/log/as
terisk/event_log
Jul 24 18:00:02 VERBOSE[20390] logger.c: == Parsing ‘/etc/asterisk/dnsmgr.conf’:
Jul 24 18:00:02 VERBOSE[20390] logger.c: == Parsing ‘/etc/asterisk/dnsmgr.conf’
: Found
Jul 24 18:00:02 VERBOSE[20390] logger.c: Asterisk Dynamic Loader loading preload m
odules:
Jul 24 18:00:02 VERBOSE[20390] logger.c: == Parsing ‘/etc/asterisk/modules.conf’
: Jul 24 18:00:02 VERBOSE[20390] logger.c: == Parsing ‘/etc/asterisk/modules.con
f’: Found
Jul 24 18:00:02 VERBOSE[20390] logger.c: == Manager registered action Ping
Jul 24 18:00:02 VERBOSE[20390] logger.c: == Manager registered action Events
Jul 24 18:00:02 VERBOSE[20390] logger.c: == Manager registered action Logoff
Jul 24 18:00:02 VERBOSE[20390] logger.c: == Manager registered action Hangup

I’m searching on Google, but i didn’t find anything for this issue…
Thanks a lot for help!