The user redeployed the target file system and verified it's contents. Afterwards the ZSMSTART STC came up without error.
This is basically equivalent to an MVS abend S806 module not found. This indicates that either a file system is not mounted, the STC / ACID assigned to the task does not have permissions to access the path, or the path does not exist.
In this case the file system was not mounted due to an IPL of the system but the BPXPRMXX member had not been updated to mount the ESM USS files at IPL time.
Update the BPXPRMXX member and all is resolved.