I noticed this when trying to apply some skin MATs.  The first one is Lindy Montana for V4 and another that shows the problem is Nanami for V4.  When the skin texture is applied via the MAT pose, there are cracks in the skin texture above the knees, at the shins, and shoulders.

Is this a result of poor skin textures?  Since it's happening with multiple skin textures that doesn't seem likely.  Photo is linked (BEWARE NUDITY.)

This happens if the MAT is applied to a zeroed figure, or to a posed figure, any time it's applied to V4 morphed or unmorphed.

Can anyone help by giving a reason and solution?

I'm also curious about this, I've seen the same thing on multiple V4 textures.  At first I thought it was just a preview thing, but they show up in the renders too.  Anyone have any advice?

Turn off texture filtering or turn up the quality :)

Never seen it happen in P6, if that's any help.  

The only thing which comes to mind is maybe it's a texture size problem (ie, too low)  or something else in your render settings.

BTW, I've added the Nudity flag on your post. 

Rendering in higher quality worked.

Also turning off texture filtering in the effected area, if rendering with lower settings for a quick test render, worked.

Not sure about texture size as I don't know how to change it.  Can someone explain?

Thanks for the quick help, BTW.

you often get that in the preview or a low quality render - bump the render slider to the right and they should go away

You can change the texture size in the advanced render settings.

Sometimes when you bake a texture set , the border will be just a couple pixels shy thus giving you a fine line where they dont quite  meet. i make it a habit of going along the edge of all textures and widening it just a bit.. This seems to cure the problem.

Gotta love those seams! They normally only show up in preview but if they're showing up in renders you need to bump up your render settings, change the minimum shading rate from it's default 1.0 to something between 0.5 & 0.2 & turn off texture filtering while you're at it.