Svchost.exe is utilized by many applications duding windows boot-up with different load parameters.
One of the best things to do is a registry search for all the entries associated with svchost.exe. Most of the entries should be native Windows applications using the program. If you see an entry that svchost.exe is being called upon, and you cannot identify: The original application that created the entry was removed but the registry key exist; that will trigger an error message.
Then svchost.exe will execute an error due to the missing application parameter it was called upon to modify, or load and no longer exist.
I am willing to bet that a Norton System Works registry key exist, and with a svchost.exe parameter present; delete the entry, or entire registry key, and re-boot and see if this sis the culprit.
Always backup, or export the registry key you will be deleting, in case you need it back.
JR