Without having more information it is hard to say what is at the root of this issue. It could be many things but a process of elimination may be in order to help eliminate possibilities.

First I would disable Tamper Protection to rule it out.

     To Disable Tamper Protection

1. Log into the Symantec Endpoint Protection Manager
2. Click on the Clients page
3. Select the group 
4. Click on the Policies tab
5. Click on General Settings ( Note: If this group is inheriting settings you will need to highlight the top level group)
6. Click on the Tamper Protection tab
7. Uncheck Protect Symantec security software from being tampered with or shut down
8. Apply the update
9. Reboot the client

   Note: You can also disable the SPBBCDRv driver in the device manager
   Note: If this resolves the issue you could also try to set exclusions for tamper protection

    

If that does not resolve the issue, next I would disable a single portion of the product one by one, testing each time, to determine which piece is the cause. For example I would first start by disabling (or uninstalling) Network Threat Protection and rebooting to test, if the issue persists then I would disable Proactive Threat Protection and test, and finally I would disable AutoProtect and test.

     To Disable Network Threat Protection

1. Log into the Symantec Endpoint Protection Manager
2. Click on the Clients page
3. Right-click on the desired group 
4. Choose Run Command on Group
5. Select Disable Network Threat Protection
    

     To Disable Proactive Threat Protection

1. Log into the Symantec Endpoint Protection Manager
2. Click on the Clients page
3. Select the group 
4. Click on the Policies tab
5. Click on Tasks and then Edit Policy across from the Antivirus and Antispyware policy
6. Click on TruScan Proactive Threat Scans on the left-hand side
7. Uncheck Scan for trojans and worms
8. Uncheck Scan for keyloggers
9. Click OK
    

     To Disable AutoProtect

1. On the local client right-click on the shielt in the taskbar
2. Choose Disable Symantec Endpoint Protection

Once you know what piece of the product is at cause you can hone in your sights to know what settings need to be adjusted.