Are you using the application and device control policy? If so, disable it.
Also, what version are you on? If 11.0.5, you will want to upgrade to the latest version, RU6 MP1.
There was an issue when upgrading to RU5 and using the app and device control policy. Upgrading to the latest version will fix this.
Release Update 6 Maintenance Patch 1 (RU6 MP1)
What's new in this version
Symantec Endpoint Protection RU6 MP1 (11.0.6100) provides fixes since the release of RU6 and RU6a. This maintenance patch cannot be installed over any versions of Symantec Endpoint Protection or Symantec Endpoint Protection Manager prior to RU6. It must be installed over RU6 or RU6a.
RU6 MP1 fixed this error:
Blue screen error referencing sysplant.sys
Fix ID: 2017143
Symptom: Computer experiences blue screen error referencing sysplant.sys.
Solution: Application and Device Control was updated to prevent the crash.