After staring/restarting Symantec Protection Engine (SPE) service the service appears up but is not listening on the configured port. A review of the <SPE_INSTALL_FOLDER>/SymantecProtectionEngineAbortLog.txt shows entries similar to the following.
400 CSAPI failed to initialize : Failed to get virtual definitions from Controller service.
0 Symantec Protection Engine is shutting down; logs may contain more information.
SPE 9.x introduced "virtual definitions" which allowed a separate "controller" service to handle virus definitions updates instead of the SPE process. If the port used by the "controller" service is already in use, then the "controller" service and SPE will be unable to communicated causing the errors noted above.
Disabling the "virtual definitions" will cause the SPE service to handle virus definition updates and will disable the "controller" service. The "virtual definitions" can be disabled by performing the following steps.
./xmlmodifier -s /configuration/Resources/System/VirtualHome/@enabled false configuration.xml