Error when importing mesh

When importing the mesh I receive this error message 

The Sims 4 Studio - Version 3.1.3.2
System.AggregateException: One or more errors occurred. ---> S4Studio.Blender.BlenderException:
File "<string>", line 1, in <module>
File "<string>", line 39, in <module>
File "C:\Users\[UserName]\AppData\Roaming\Blender Foundation\Blender\2.70\scripts\addons\s4studio\cas\blender.py", line 122, in save_geom
weight_list[blend_index_map] = min(int(vertex.groups.weight * 255), 255)
ValueError: cannot convert float NaN to integer


at S4Studio.Blender.BlenderUtilities.RunBlender(String script, String blend, Boolean background, Boolean check_version)
at S4Studio.Blender.BlenderUtilities.ImportGeom(String custom_blend, String custom_geom, Int32 body_type, String cut)
at S4Studio.ViewModels.CAS.CASLODItem.ImportMesh(BlenderUtilities blender_util, String blender_path)
at S4Studio.ViewModels.CAS.CASStandalone.<>c__DisplayClass71_0.<ExecuteImportMesh>b__0()
at System.Threading.Tasks.Task.InnerInvoke()
at System.Threading.Tasks.Task.Execute()
--- End of inner exception stack trace ---
---> (Inner Exception #0) S4Studio.Blender.BlenderException:
File "<string>", line 1, in <module>
File "<string>", line 39, in <module>
File "C:\Users\[UserName]\AppData\Roaming\Blender Foundation\Blender\2.70\scripts\addons\s4studio\cas\blender.py", line 122, in save_geom
weight_list[blend_index_map] = min(int(vertex.groups.weight * 255), 255)
ValueError: cannot convert float NaN to integer


at S4Studio.Blender.BlenderUtilities.RunBlender(String script, String blend, Boolean background, Boolean check_version)
at S4Studio.Blender.BlenderUtilities.ImportGeom(String custom_blend, String custom_geom, Int32 body_type, String cut)
at S4Studio.ViewModels.CAS.CASLODItem.ImportMesh(BlenderUtilities blender_util, String blender_path)
at S4Studio.ViewModels.CAS.CASStandalone.<>c__DisplayClass71_0.<ExecuteImportMesh>b__0()
at System.Threading.Tasks.Task.InnerInvoke()
at System.Threading.Tasks.Task.Execute()<---