That does seem a bit large. What are the triangle, limb, and bone counts?
some quick googling
site:forum.thegamecreators.com error 7018
https://www.google.com/search?q=site%3Aforums.thegamecreators.com+error+7018&ie=utf-8&oe=utf-8#q=site:forum.thegamecreators.com+error+7018
seems to suggest that it is likely an issue with the .x exporter formatting or export settings.
Make sure that you do not have any ngons: use triangles and quads only.
If you have bones, ensure every vertex is assigned to at least one bone, but no more than 4 bones per vertex, and ensure that every bone has at least one vertex
You may need to ensure that the model is being exported with UV data.
http://games.joshkirklin.com/sulium
A single player RPG featuring a branching, player driven storyline of meaningful choices and multiple endings alongside challenging active combat and intelligent AI.