This could be triggered by either TruScan or Network Threat Protection.
How to add a TruScan exception:
Open Symantec Endpoint Protection
Select Change Settings in the left pane
Click the Configure Settings button across from Centralized Exceptions
In the User-Defined Exceptions tab, select Add...
Select TruScan Proactive threat Scan Exception
Browse to C:\WINDOWS\system32\
Select ntoskrnl.exe
Choose the desired action from the Action drop down menu
Note: For testing purposes choose "Log only"
Click Add
Close the Centralized Exceptions window.
If the TruScan exception does not resolve the issue, test by adding a Firewall rule
How to add a Firewall rule:
Open Symantec Endpoint Protection
Click the Options button across from Network Threat Protection
Select Configure Firewall Rules...
Click Add...
Type in a rule name
Under Action select Allow this traffic
Click the Applications tab
Click Browse...
Navigate to C:\WINDOWS\system32\
Select ntoskrnl.exe
Click Open
Click OK
Highlight the rule in the list
Click the up arrow button to move the rule to the top of the list
Click OK
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You may try this as well :
1.Login into your Symantec Endpoint Protection Manager.
2.Click on Policies - Intrusion Prevention - edit your Intrusion Prevention policy
3.Click on Settings
4.Tick the "Enable excluded hosts" option and click on the Excluded Hosts button to add your ip address (or a range of ip address, alternatively you could also use the subnet option).