I've never used that product from Norton, so I am just assuming it is walking the registry and looking for references to files that no longer exist. It's hard to say how important this particular report is. I wouldn't sweat it too much until something fails to work or gives an error message. That DLL is the Microsoft C runtime library for version 8.0. It includes a lot of basic functions that C programs use. Many programs link these functions in statically, and don't require the DLL version. Others use the DLL to save space. If you have entries to it in the registry they could be programs storing the DLL location, or they could be entries for MS tools that didn't get cleaned up. Could be anything really. Programs that use the C runtime in DLL form usually distribute it with the application, and either copy it to the system directory, or place it in their own program directories.
One thing to try is use Explorer and search for the file across your whole drive. I would also compare the paths that Norton is reporting as being missing. Do they all point to the same spot? If you have a program fail to work, then simply
downloading the file and copying it to the program directory should work.