How to shorten a mesh in blender

I tried to follow your directions on how to shorten a long dress. I thought I had it figured out:

I think I understood when you said to delete all but a vertex of unused meshes:

But I get this error message when I try to import the LOD:

The Sims 4 Studio - Version 2.3.0.2
System.AggregateException: One or more errors occurred. ---> S4Studio.Blender.BlenderException: Traceback (most recent call last):
File "<string>", line 1, in <module>
File "<string>", line 52, in <module>
File "C:\Users\[UserName]\AppData\Roaming\Blender Foundation\Blender\2.70\scripts\addons\s4studio\cas\blender.py", line 44, in save_geom
mesh_data.calc_tangents()
RuntimeError: Error: Tangent space computation needs an UVMap, "(null)" not found, aborting


at S4Studio.Blender.BlenderUtilities.RunBlender(String script, String blend, Boolean background, Boolean check_version) in c:\Workspace\Sims4Studio\TheS4Studio\S4Studio.Blender\BlenderUtilities.cs:line 238
at S4Studio.Blender.BlenderUtilities.ImportGeom(String custom_blend, String custom_geom, Int32 body_type, String cut) in c:\Workspace\Sims4Studio\TheS4Studio\S4Studio.Blender\BlenderUtilities.cs:line 335
at S4Studio.MainWindow.<>c__DisplayClass33.<ImportFromBlenderButton_OnClick>b__32() in c:\Workspace\Sims4Studio\TheS4Studio\S4Studio\UI\MainWindow.xaml.cs:line 705
at S4Studio.LoadingScreen.<>c__DisplayClass2.<Show>b__0() in c:\Workspace\Sims4Studio\TheS4Studio\S4Studio\UI\LoadingScreen.xaml.cs:line 39
at System.Threading.Tasks.Task.InnerInvoke()
at System.Threading.Tasks.Task.Execute()
--- End of inner exception stack trace ---
at S4Studio.LoadingScreen.<>c__DisplayClass2.<Show>b__1() in c:\Workspace\Sims4Studio\TheS4Studio\S4Studio\UI\LoadingScreen.xaml.cs:line 48
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
---> (Inner Exception #0) S4Studio.Blender.BlenderException: Traceback (most recent call last):
File "<string>", line 1, in <module>
File "<string>", line 52, in <module>
File "C:\Users\[UserName]\AppData\Roaming\Blender Foundation\Blender\2.70\scripts\addons\s4studio\cas\blender.py", line 44, in save_geom
mesh_data.calc_tangents()
RuntimeError: Error: Tangent space computation needs an UVMap, "(null)" not found, aborting


at S4Studio.Blender.BlenderUtilities.RunBlender(String script, String blend, Boolean background, Boolean check_version) in c:\Workspace\Sims4Studio\TheS4Studio\S4Studio.Blender\BlenderUtilities.cs:line 238
at S4Studio.Blender.BlenderUtilities.ImportGeom(String custom_blend, String custom_geom, Int32 body_type, String cut) in c:\Workspace\Sims4Studio\TheS4Studio\S4Studio.Blender\BlenderUtilities.cs:line 335
at S4Studio.MainWindow.<>c__DisplayClass33.<ImportFromBlenderButton_OnClick>b__32() in c:\Workspace\Sims4Studio\TheS4Studio\S4Studio\UI\MainWindow.xaml.cs:line 705
at S4Studio.LoadingScreen.<>c__DisplayClass2.<Show>b__0() in c:\Workspace\Sims4Studio\TheS4Studio\S4Studio\UI\LoadingScreen.xaml.cs:line 39
at System.Threading.Tasks.Task.InnerInvoke()
at System.Threading.Tasks.Task.Execute()<---

I'm a complete noob at meshing, and the only thing I see that I understand is something about a missing UV map, but I don't know what's missing:

Any help you can give would be greatly appreciated!!!

Edit: Is there any reason why I'd have to do a UV map for the two meshes I deleted all but one vertex on? And if so, how do you do a UV map on a single vertex? Or is that a completely stupid suggestion?

Thanks OM, that was EXACTLY what I needed!

 I was thinking maybe I didn't know what a vertex was, because it seemed to me that I should probably leave a triangle, but I thought that was what's called a face, so I didn't do it. My self-doubt got the best of me. I still need to try it out in game, but at least it's showing up in S4S, so I'm very happy to see forward progress!