Symptom:
********************* CRASH #01 ***********************
SW Version          : 16.1(55634)
Similar Crash Count : 1
Time of First Crash : 2014-Aug-07+22:58:21

Assertion failure at sess/mme/mme-app/app/mme_pdn_connect_proc.c:689
  Function: mme_pdn_connect_send_csr()
  Expression: (((ue_enb) != ((void *)0)) && ((ue_enb)->uec_magic == (('M'<<24)|('U'<<16)|('E'<<8)|('C'))))
  Proclet: sessmgr (f=87000,i=47)
  Process: card=6 cpu=0 arch=X pid=5249 cpu=~1% argv0=sessmgr
  Crash time: 2014-Aug-08+02:58:21 UTC
  Recent errno: 11 Resource temporarily unavailable
  Stack (60184@0xfffef000):
    [ffffe430/X] __kernel_vsyscall() sp=0xfffeff78
    [0abbbd9f/X] sn_assert() sp=0xfffeffb8
    [07cd9577/X] mme_pdn_connect_send_csr() sp=0xffffc088
    [07cdf5ca/X] mme_pdn_connect_awt_dns_pgw_rsp() sp=0xffffc3e8
    [07c6de52/X] mme_fsm_event_handler() sp=0xffffc898
    [07c9a3fa/X] mme_event_handler_pdn_connect_procedure() sp=0xffffc8e8
    [07b7cc90/X] mme_procedure_handle_event() sp=0xffffc968
    [07c6f582/X] mme_disp_handle_pdn_evt() sp=0xffffca58
    [07c9f3d2/X] mme_disp_attached_handle_dns_rsp() sp=0xffffca98
    [07c6de52/X] mme_fsm_event_handler() sp=0xffffcf48
    [07c98ef6/X] mme_app_pgw_dns_rsp_cb() sp=0xffffd028
    [08ab1849/X] snaptr_procedure_complete.part.2() sp=0xffffd488
    [08aaa82d/X] async_return_cbk() sp=0xffffd4c8
    [051858e0/X] tlib_serv() sp=0xffffd518
    [0518558c/X] tlib_tmr_tick() sp=0xffffd568
    [045dfb52/X] snx_timer_service() sp=0xffffd578
    [045dda5f/X] snx_fast_service() sp=0xffffd5a8
    [05d6e5ba/X] sessmgr_snx_tick_callback() sp=0xffffd5e8
    [0ac5a189/X] sn_loop_run() sp=0xffffda98
    [0a9fd66d/X] main() sp=0xffffdb08

Conditions:
When a PDN connect is received while idle mode exit is in progress and is not complete and it gets context seto failure response. Here is the sequence of events that leads to the crash

i) UE is in idle mode
ii) UE issues service request for exit from idle mode.
iii) MME issues context setup request 
iv) Before MME gets context setup response, MME gets a PDN connect. This PDN connect gets queued as MME is not completed processing for IM exit procedure.
v) MME receives context setup failure response. 

If MME is configured to move the UE back to idle mode on context setup failure - "policy service-request initial-context-setup-failure s1ap-cause-code-group s1ap_ccg_idle action idle-mode-entry", MME crashes while processing the outstanding PDN connect.