Error Message Importing Mesh to S4S Mac (Appletini)

Hello!! I just finished editing an EA mesh in Blender (2.78) and I am trying to import it back into Sims 4 Studio and I keep getting an error message. Can anyone tell me what this means??? Thanks so much !

Sims 4 Studio 1.1.0.5 (Appletini)
S4Studio.Blender.BlenderException:
File "/Users/[UserName]/.local/share/S4Studio/Scripts/geomexporter.py", line 41, in <module>
geom.write(output_stream)
File "/Users/[UserName]/Library/Application Support/Blender/2.78/scripts/addons/s4studio/io.py", line 626, in write
rcol.get_block_index(self, self.ROOT_REFERENCE_TYPE)
File "/Users/[UserName]/Library/Application Support/Blender/2.78/scripts/addons/s4studio/io.py", line 525, in get_block_index
block.write_rcol(stream, self)
File "/Users/[UserName]/Library/Application Support/Blender/2.78/scripts/addons/s4studio/cas/geometry.py", line 423, in write_rcol
write_vertex_data(declaration, s, vertex.blend_weights)
File "/Users/[UserName]/Library/Application Support/Blender/2.78/scripts/addons/s4studio/cas/geometry.py", line 397, in write_vertex_data
s.u8(element)
File "/Users/[UserName]/Library/Application Support/Blender/2.78/scripts/addons/s4studio/io.py", line 228, in u8
self.u(data, 8, order)
File "/Users/[UserName]/Library/Application Support/Blender/2.78/scripts/addons/s4studio/io.py", line 209, in u
if size == 8: self.write('B', data, order)
File "/Users/[UserName]/Library/Application Support/Blender/2.78/scripts/addons/s4studio/io.py", line 183, in write
self.f.write(struct.pack(l, data))
struct.error: ubyte format requires 0 <= number <= 255


at S4Studio.Blender.BlenderUtilities.RunBlender (System.String script, System.String blend, System.Boolean background, System.Boolean check_version) [0x00392] in /Users/A/Desktop/S4S/TheS4Studio/S4Studio.Shared/BlenderUtilities.cs:248
at S4Studio.Blender.BlenderUtilities.ImportGeom (System.String custom_blend, System.String custom_geom, System.Int32 body_type, System.String cut) [0x00099] in /Users/A/Desktop/S4S/TheS4Studio/S4Studio.Shared/BlenderUtilities.cs:361
at S4Studio.ViewModels.CAS.CASLODItem.ImportMesh (S4Studio.Blender.BlenderUtilities blender_util, System.String blender_path) [0x0014b] in /Users/A/Desktop/S4S/TheS4Studio/S4Studio.Shared/ViewModels/CAS/CASLODItem.cs:192
at S4Studio.ViewModels.CAS.CASStandalone+<>c__DisplayClass71_0.<ExecuteImportMesh>b__0 () [0x0000d] in /Users/A/Desktop/S4S/TheS4Studio/S4Studio.Shared/ViewModels/CAS/CASStandalone.cs:417
at S4S.UI.Core.S4SWindow+<>c__DisplayClass10_0.<BeginLoading>b__1 () [0x00016] in /Users/A/Desktop/S4S/TheS4Studio/S4Studio.Mac/UI/Core/S4SWindow.cs:154