When I try and use this theme, I get about 50 error messages about not finding "IconDir" and some other directories. However, the theme does load and seems to function properly, but I would like to find a way to fix this.

Thanks.

Open up your filemanager,
Start a new search on the theme directory,
Choose "Find text inside file" or whatever it is,
Search for "IconDir",

It will most probably be inside the theme.rc file though,
Something like:

IconDir "$ThemeDir$Misc"

You need to change it so it points to an actual folder.

OR

IconDir is actually not defined.
In which case you need to find the folder with the icons (lets say its "$ThemeDir$misc\icons\")

and add an evar definition to the theme.rc:

IconDir "$ThemeDir$misc\icons\"

this should fix it...