When the Group Update Provider (GUP) functionality is enabled on a Symantec Endpoint Protection Client between versions 12.1 RU4 (12.1.4013.4013) and 12.1 RU4 MP1b (12.1.4112.4156), the Symantec Management Client process (SMC.exe) crashes. If the GUP functionality is disabled, the crash no longer occurs.
This issue has been resolved in 12.1 RU5 (12.1.5337.5000). Upgrade your GUPs to 12.1 RU5 to resolve this issue.
Symantec Endpoint Protection version 12.1 RU4 (12.1.4013.4013) through 12.1 RU4 MP1b (12.1.4112.4156).