IHS session串号问题求助

一个IHS下拖了6个server，偶尔出现A的sessioin串到B的session情况。有专家知道是咋回事吗？另外IHS plugin日志中报了很多异常信息：
[Mon Jun 16 06:17:12 2014] 00005f77 c0b76b90 - ERROR: ws_server_group: NewserverGroupNextRoundRobinServer: Failed to find a server in group Cluster01; all could be down or have reached the maximimum connections limit
[Mon Jun 16 06:17:12 2014] 00005f77 c0b76b90 - ERROR: ws_common: websphereFindServer: Failed to find a server
[Mon Jun 16 06:17:12 2014] 00005f77 c0b76b90 - ERROR: ws_common: websphereWriteRequestReadResponse: Failed to find a server
[Mon Jun 16 06:17:12 2014] 00005f77 c0b76b90 - ERROR: ESI: getResponse: failed to get response: rc = 4
[Mon Jun 16 06:17:12 2014] 00005f77 c0b76b90 - ERROR: ws_common: websphereHandleRequest: Failed to handle request
[Mon Jun 16 06:17:12 2014] 00005f77 c657fb90 - ERROR: ws_server_group: NewserverGroupNextRoundRobinServer: Failed to find a server in group Cluster01; all could be down or have reached the maximimum connections limit
[Mon Jun 16 06:17:12 2014] 00005f77 c657fb90 - ERROR: ws_common: websphereFindServer: Failed to find a server
[Mon Jun 16 06:17:12 2014] 00005f77 c657fb90 - ERROR: ws_common: websphereWriteRequestReadResponse: Failed to find a server
[Mon Jun 16 06:17:12 2014] 00005f77 c657fb90 - ERROR: ESI: getResponse: failed to get response: rc = 4
[Mon Jun 16 06:17:12 2014] 00005f77 c657fb90 - ERROR: ws_common: websphereHandleRequest: Failed to handle request
[Mon Jun 16 06:17:12 2014] 00005f77 d919db90 - ERROR: ws_server_group: NewserverGroupNextRoundRobinServer: Failed to find a server in group Cluster01; all could be down or have reached the maximimum connections limit
[Mon Jun 16 06:17:12 2014] 00005f77 d919db90 - ERROR: ws_common: websphereFindServer: Failed to find a server
[Mon Jun 16 06:17:12 2014] 00005f77 d919db90 - ERROR: ws_common: websphereWriteRequestReadResponse: Failed to find a server
[Mon Jun 16 06:17:12 2014] 00005f77 d919db90 - ERROR: ESI: getResponse: failed to get response: rc = 4
[Mon Jun 16 06:17:12 2014] 00005f77 d919db90 - ERROR: ws_common: websphereHandleRequest: Failed to handle request
[Mon Jun 16 06:17:12 2014] 00005f77 deba6b90 - ERROR: ws_server_group: NewserverGroupNextRoundRobinServer: Failed to find a server in group Cluster01; all could be down or have reached the maximimum connections limit
[Mon Jun 16 06:17:12 2014] 00005f77 deba6b90 - ERROR: ws_common: websphereFindServer: Failed to find a server
[Mon Jun 16 06:17:12 2014] 00005f77 deba6b90 - ERROR: ws_common: websphereWriteRequestReadResponse: Failed to find a server
[Mon Jun 16 06:17:12 2014] 00005f77 deba6b90 - ERROR: ESI: getResponse: failed to get response: rc = 4
[Mon Jun 16 06:17:12 2014] 00005f77 deba6b90 - ERROR: ws_common: websphereHandleRequest: Failed to handle request
[Mon Jun 16 06:17:12 2014] 00005f77 dcda3b90 - ERROR: ws_server_group: NewserverGroupNextRoundRobinServer: Failed to find a server in group Cluster01; all could be down or have reached the maximimum connections limit
[Mon Jun 16 06:17:12 2014] 00005f77 dcda3b90 - ERROR: ws_common: websphereFindServer: Failed to find a server
[Mon Jun 16 06:17:12 2014] 00005f77 dcda3b90 - ERROR: ws_common: websphereWriteRequestReadResponse: Failed to find a server
[Mon Jun 16 06:17:12 2014] 00005f77 dcda3b90 - ERROR: ESI: getResponse: failed to get response: rc = 4
[Mon Jun 16 06:17:12 2014] 00005f77 dcda3b90 - ERROR: ws_common: websphereHandleRequest: Failed to handle request
[Mon Jun 16 06:17:13 2014] 00005f77 ec7bcb90 - ERROR: ws_server_group: NewserverGroupNextRoundRobinServer: Failed to find a server in group Cluster01; all could be down or have reached the maximimum connections limit
[Mon Jun 16 06:17:13 2014] 00005f77 ec7bcb90 - ERROR: ws_common: websphereFindServer: Failed to find a server
[Mon Jun 16 06:17:13 2014] 00005f77 ec7bcb90 - ERROR: ws_common: websphereWriteRequestReadResponse: Failed to find a server