brianjgorman wrote: I get an error message that says "unable to load required library."
Are you talking about the Library of sounds supplied by Sibelius? Or some other VSTi?
Where is the library? Sibelius, if properly installed, should know where look for the library, though in the Play > Playback Devices > Audio Engine Options
dialog you can get it to search, just in case you installed it somewhere non-standard.
Converting from the Demo — not a process with which I am familiar —might not tell Sibelius that it has its library (the Demo doesn't have it, so it knows not to look for it).
What a shame you lost the installation disk (which is, as it happens, a DVD-ROM rather than a CD-ROM) so soon after purchasing it. The Sibelius Sounds library can be installed separately from that disk — perhaps you didn't take this essential step when you first installed.