Looking at the comments on that addon's page, I would guess it's abandoned, since there is a post from back in August noting that it was broken back then, and there was neither an update nor a response from the author.
From the description on the SilverDragon download page:
If you have ... HandyNotes installed it will add map notes for rares, which can be shared with others.
HandyNotes is a general-purpose "map notes" addon. It's compatible with all addons that modify the world map, and with the default world map. You can create your own notes by hand, and there are many addons that will create notes through it, including SilverDragon.
After you install HandyNotes, import the default data from SilverDragon (it's in the SilverDragon options). If I recall correctly, this is when it adds icons to the map (been a while since I initially imported it, so sorry if this info is incorrect).
I recommend NPCScan.Overlay. In my opinion better than Rare Spawn Overlay since it will show locations on the minimap as well. Offcourse it integrates well with NPCScan (which I recommend as well).
edit: also works with Carbonite if you are using that.
Agreed, the addon NPCScan and also get NPCScan Overlay not ony auto tracks rares, ie. dont have to smash buttons to find them, but also has a map overlay that shows the spot or areas that the rare is "known" to be found. For those zones that you are able to fly in, simply fly over the map in the overlay area and hope you find one, that simple. Hope this helps