Hello,
Upon checking th esylink.log, we found -
10/31 13:49:32 [3400] <Start>Unable to create Session with 'User Proxy' settings - Proxy Server: Error Code: 87
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10/31 13:53:02 [2736] <PostEvent>going to post event=EVENT_SERVER_DISCONNECTED
10/31 13:53:02 [2736] <PostEvent>done post event=EVENT_SERVER_DISCONNECTED, return=0
10/31 13:53:02 [2736] <IndexHeartbeatProc>====== IndexHeartbeat Procedure stops at 13:53:02 ======
10/31 13:53:02 [2736] <IndexHeartbeatProc>Set Heartbeat Result= 1
10/31 13:53:02 [2736] <IndexHeartbeatProc>Sylink Comm.Flags: 'Connection Failed' = 1, 'Using Backup Sylink' = 0, 'Using Location Config' = 0
10/31 13:53:02 [2736] <IndexHeartbeatProc>Connection Failed! No. of tries = 3
10/31 13:53:02 [2736] <SwitchSylinkConfig:> Switching from sylink.xml..
10/31 13:53:02 [2736] <SwitchSylinkConfig:> Failed to switch to use SyLinkEx.bak
10/31 13:53:02 [2736] <SwitchSylinkConfig:> Switching from SyLinkEx.bak
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10/31 13:57:18 [2736] <mfn_DoGetIndexFile200>Content Lenght => 1368
10/31 13:57:18 [2736] <mfn_DoGetIndexFile200>Signature verification FAILED for Index File Content..
10/31 13:57:18 [2736] <GetIndexFileRequest:>RECEIVE STAGE COMPLETED
10/31 13:57:18 [2736] <GetIndexFileRequest:>COMPLETED
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10/31 13:57:18 [2736] <PostEvent>going to post event=EVENT_SERVER_DISCONNECTED
10/31 13:57:18 [2736] <PostEvent>done post event=EVENT_SERVER_DISCONNECTED, return=0
10/31 13:57:18 [2736] <IndexHeartbeatProc>====== IndexHeartbeat Procedure stops at 13:57:18 ======
10/31 13:57:18 [2736] <IndexHeartbeatProc>Set Heartbeat Result= 1
10/31 13:57:18 [2736] <IndexHeartbeatProc>Sylink Comm.Flags: 'Connection Failed' = 1, 'Using Backup Sylink' = 1, 'Using Location Config' = 0
10/31 13:57:18 [2736] <IndexHeartbeatProc>Connection Failed! No. of tries = 1
10/31 13:57:18 [2736] Use new configuration
10/31 13:57:18 [2736] HEARTBEAT: Check Point Complete
10/31 13:57:18 [2736] <IndexHeartbeatProc>Done, Heartbeat=512seconds
As per above, It's definitely the certificate issue, restore the certifcate of older time and it should help.
Check these Articles:
Signature verification FAILED for Index File Content - Clients are green in the SEPM, but show offline.
http://www.symantec.com/docs/TECH93740
Symantec Endpoint Protection Signature verification FAILED for Index File Content
http://www.symantec.com/docs/TECH102900
Hope that helps!!