Well, I (or better I say GoaFan did it for me) tried to convert a xsi model to mesh, and the result was that:
Ignoring unknown material type (24): DefaultLib.Scene_Material
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh1ClsMaterial4
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh1ClsMetal_Aluminum_Co
rrugated
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh1ClsM_0135_DarkGray
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh1ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh1ClsFrontColor
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh2ClsFrontColor
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh2ClsM_0111_SlateGray
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh2ClsM_0133_Gray
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh2ClsM_0135_DarkGray
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh2ClsMaterial1
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh2ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh2ClsMaterial4
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh2ClsMaterial5
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh2ClsMaterial6
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh2ClsMetal_Aluminum_Co
rrugated
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh3ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh4ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh5ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh6ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh7ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh8ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh9ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh10ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh11ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh12ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh13ClsMaterial3
Ignoring unknown material type (24): Mon_Calamari_MC75.Mesh14ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh1ClsMaterial4
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh1ClsMetal_Alumin
um_Corrugated
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh1ClsM_0135_DarkG
ray
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh1ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh1ClsFrontColor
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh2ClsFrontColor
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh2ClsM_0111_Slate
Gray
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh2ClsM_0133_Gray
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh2ClsM_0135_DarkG
ray
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh2ClsMaterial1
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh2ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh2ClsMaterial4
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh2ClsMaterial5
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh2ClsMaterial6
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh2ClsMetal_Alumin
um_Corrugated
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh3ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh4ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh5ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh6ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh7ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh8ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh9ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh10ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh11ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh12ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh13ClsMaterial3
Valid Material not found for PolygonList: Mon_Calamari_MC75.Mesh14ClsMaterial3
Point found: 'Above'
Point found: 'Aura'
Point found: 'Center'
Point found: 'Weapon-0'
Point found: 'Weapon-0'
Point found: 'Weapon-0'
Point found: 'Weapon-0'
Point found: 'Exhaust'
Point found: 'Exhaust1'
Bounding Information Calculated - Radius:-1.00
Optimizing...
Pre-Optimization Vertex Count = 0
Post-Optimization Vertex Count = 0
What sould tell me this? 
