Well, If you're 100% positive you don't have net framework, (it WAS a
downloadable option in Windows Updates) - then I can't help.
BTW, you don't "go into" .net framework, (nor do you get it from a CD or DVD
of all things) - & once it's installed it becomes part of your system, which
gives me the impression you're completely ignorant as to whether you have it
or not.
Did you actually CHECK in Add/Remove Programs for "Microsoft Net Framework"
as advised?
Also, if you're really convinced that the Symantec upgrade caused that error
message (you didn't even mention which particular Symantec program you
upgraded), check with them.