I'm sure it's a different problem.

The Unimesh skinning needed for SubD quickly reveals unwelded vertices.

To fix it, you have to export the whole mesh out of Poser, as you can't weld a single bodypart to a figure inside Poser.

Make sure Katie is completely zeroed.

Export her.

Import her into Wings3D.

Fix the hand the same way you already did. DO NOT MOVE/SCALE OR OTHERWISE ALTER THE REST OF THE MESH.

Do not move the hand either, or Poser won't be able to weld Katie back into a figure.

Export everything and replace the original object file with the fixed one.

(Make a backup first to be sure !)

Restart Poser and if you did everything correctly, the problem should be gone.

BUT...You changed the vertex count for the hand, so any previous morphs for it won't work anymore.