I’ve run into this issue before and what I did was select my model, go into edit mode. Then I hit A to select everything. CTRL + T to triangulate the mesh (turns quads into triangles). And then with everything still selected, ALT + J to turn triangles back to quads. You should be able to export now.
I think you get that error when you have any NGons (5 verts or more). The trick above should fix that.