I took a look at my Civ3 Complete install and that scenario, and sure enough, it looks like Firaxis didn't ship some files that that scenario needs, including that one. I unfortunately don't know the origin of viriato.flc. But you can copy files and rename them such that the game will see them.
The game is looking for a file called viriato.flc in the folder <Civ3 Complete Installation Directory>\civ3PTW\Scenarios\Ancient Mediterranean\Art, such as C:\Program Files\2K Games\Civilization III Complete\civ3PTW\Scenarios\Ancient Mediterranean\Art. This file (along with other flc files) would normally be in a folder named "Flics", but that folder doesn't exist. You'll need to create it. Then go to <Civ3 Complete Installation Directory>\civ3PTW\Art\Flics, and copy x_isabell diplo mid fwrd.flc (or any of the files really) into <Civ3 Complete Installation Directory>\civ3PTW\Scenarios\Ancient Mediterranean\Art, and rename it viriato.flc.
If you open the scenario in the editor, and look at the Civilizations, specifically the Animations section, you'll find several more files that don't exist, such as Art\Flics\pericles.flc for the Greeks, and Art\Flics\arminus.flc for the Germanic Tribes. You'll need to copy over and rename a .flc file for each of these, too. It doesn't really matter which .flc file you copy (that will only affect the visuals). Copying and renaming any of the .flc files will be enough to placate the game and keep it from crashing.
