GSM切换失败A口信令原因分析，求大虾支招

bgws

进行了一次关于上行质量的切换时失败，上报失败原因为Protocol error between BSC and MSC，
本次切换失败导致了掉话，请高手分析一下可能存在原因，通过仅有A口信令怎么找出问题点。
谢谢！
A口信令信令如下：（为通话结束部分）

23:24:51'027 MBSC404[9250]-->CSGS03 [BSSMAP]Handover Required ,Better cell(12)
23:24:51'151     0 CSGS03-->MBSC696[9699] [BSSMAP]Handover Request ,Better cell(12),7,8,29677,13513
23:24:51'292   141 MBSC696[9699]-->CSGS03 [DTAP]Handover Command
23:24:51'308 CSGS03-->MBSC404[9250] [DTAP]Handover Command
23:24:51'644   493 MBSC696[9699]-->CSGS03 [BSSMAP]Handover Detect
23:24:51'944   793 MBSC696[9699]-->CSGS03 [BSSMAP]Handover Complete
23:24:52'030 CSGS03-->MBSC404[9250] [BSSMAP]Clear Command ,Handover successful(11)
23:24:52'095 MBSC404[9250]-->CSGS03 [BSSMAP]Clear Complete
23:24:52'109 CSGS03-->MBSC404[9250] [SCCP_NGN]Released
23:24:52'149 MBSC404[9250]-->CSGS03 [SCCP_NGN]Release Complete
23:24:52'298  1147 MBSC696[9699]-->CSGS03 [BSSMAP]Classmark update
23:25:00'557  9406 MBSC696[9699]-->CSGS03 [BSSMAP]Handover Required ,Uplink quality(2),58358,24293
23:25:00'579  9428 CSGS03-->MBSC404[9250] [BSSMAP]Handover Request ,Uplink quality(2),6,5,29675,47512
23:25:00'722  9571 MBSC404[9250]-->CSGS03 [DTAP]Handover Command
23:25:00'726  9575 CSGS03-->MBSC696[9699] [DTAP]Handover Command
23:25:15'727 24576 CSGS03-->MBSC404[9250] [BSSMAP]Clear Command ,Protocol error between BSC and MSC(96)
23:25:15'795 24644 MBSC404[9250]-->CSGS03 [BSSMAP]Clear Complete
23:25:15'795 24644 CSGS03-->MBSC404[9250] [SCCP_NGN]Released
23:25:15'804 24653 CSGS03-->MBSC696[9699] [BSSMAP]Clear Command ,Protocol error between BSC and MSC(96)
23:25:15'817 24666 MBSC404[9250]-->CSGS03 [SCCP_NGN]Release Complete
23:25:15'843 24692 MBSC696[9699]-->CSGS03 [BSSMAP]Clear Complete
23:25:15'853 24702 CSGS03-->MBSC696[9699] [SCCP_NGN]Released
23:25:15'868 24717 MBSC696[9699]-->CSGS03 [SCCP_NGN]Release Complete