I can't include pictures for steps at the moment but I will discuss the steps I went through.

First I create (Cardigan) the mesh in Marvelous Designer 3 then export it as .obj.
Unchecked the Avatar, selected multiple objects and then scaled down the mesh to cm (Daz Studio) into .100%
then import in Maya. Selected all the faces and extruded without moving it I have merged the verticles on the seams and then correctly uv mapped, soften edges the mesh export as obj again for Milkshape
Import in Milkshape then the body rig for milkshape, regrouped them as group_base. Used mesh toolkit on auto tools for .wso with Dress reference
Import in TSRW, it's a unmatched number of vertices with group_thin xxx out of xxxx with no base group.

I tried again on new mesh a shirt, after looking up the solution NO SOFTEN EDGES AND VERTICLES MERGED AT THE SEAMS with the shirt. used the clean tool in milkshape, it still give the same issue. Any idea why? My friend went through this WITHOUT soften edges and verticles so the morph meshes import was success for her. It never worked for me except the base mesh can be imported.

When you import your mesh and TSR Workshop asks if you want to automatically update vertex data, select "no." The last time I had the problem you're describing, that worked for me.

I can't click no because the import fails when I click ok

At what step are you clicking 'ok' and get an error? What's the error message?

Can you upload your wso mesh before and after you use Toolkit on it?

I select okay when it says group_any size have unmatched number of vertices with title saying 'no base group', I have the orginal group_base when i did regroup the body and the meshes. l click ok on the dailouge box the import fails

I auto assigned the bones first then morphs with the dress reference. If i only assigned bones, it would import but morphs alone, its the same issue.

I had no problem importing the mesh in TSRW:

Start a new project, cloning a adult female top
In the Mesh tab, choose High Level of Detail
Click the Import button (icon of box with green arrow)
Select the 'after' mesh
Get a popup saying "Do you want workshop to optimize the vertex data", click No
Get a popup saying "You have imported a new mesh, do you want to update the bounding box values automatically", click Yes
Import is successful.

(I'm using TSRW Version 2.0.72. If you're using a old version it might behave differently.)

There is no step where you can click Okay, so you must be doing something else. It would save time if you'd explain exactly what you're doing and what steps you went through, not while creating the mesh but when you get the actual problem.

The WSO file with the morphs is corrupt, most likly because it is a extremly high polygon mesh.....Milkshape has no problem with the base mesh but the file with the morphs contains errors.
Try to delete one on the meshgroups, it makes MS crash.

CmarNYC, thank you so much it works! I'm glad this issue is resolved. I was going to give up lol.

BloomsBase, MS never crashed on me when I import the morphed .wso.