No we are not using Advanced Queuing?
I have restarted and disabled standby dest. Archive_log_dest_2=rest,min_suceed set to 1. Now it is working properly.

But i want to know the root cause.
Trace file at the time of err.

*** SESSION ID:(3.1) 2007-03-13 22:39:34.309
*** 2007-03-13 22:39:34.309 42161 kcrr.c
Initializing NetServer for dest=ISPRO20.STANDBY1
Initializing PGA storage for Netserver communication
Allocating a brand new NetServer
Allocated NetServer 0
Starting NetServer
NetServer 0 has been started.Subscribing to KSR Channel 0
success!
Indicating recv buffer for KSR Channel 0
success
Waiting for Netserver 0 to initialize itself
Waiting for Netserver 0 to initialize itself
Waiting for Netserver 0 to initialize itself
*** 2007-03-13 22:39:38.346 42446 kcrr.c
Netserver 0 has been initialized
LGWR performing a channel reset to ignore previous responses
LGWR connecting as publisher to KSR Channel 0
LGWR-NS 0 initialized for destination=ISPRO20.STANDBY1
*** 2007-03-13 22:39:38.346 42894 kcrr.c
Making upiahm request to NetServer 0
Waiting for NetServer to respond to upiahm
*** 2007-03-13 22:39:38.594 43080 kcrr.c
upiahm connect done status is 0
Receiving message from NetServer 0
Destination LOG_ARCHIVE_DEST_2 is in CLUSTER CONSISTENT mode
Destination LOG_ARCHIVE_DEST_2 is in MAXIMUM AVAILABILITY mode
Receiving message from NetServer 0
*** 2007-03-13 22:39:38.630 44311 kcrr.c
Making upinbls request to NetServer 0
NetServer pid:16247
*** 2007-03-13 22:39:38.630 44448 kcrr.c
upinbls done status is 0
LGWR: Waiting to hear from Network Server 0
LGWR: Waiting to hear from Network Server 0
LGWR: Waiting to hear from Network Server 0
LGWR: Waiting to hear from Network Server 0
LGWR: Waiting to hear from Network Server 0
LGWR: Waiting to hear from Network Server 0
LGWR: Waiting to hear from Network Server 0

can any one say root cause.
pls help.