Hi,
I'm remaking my t-shirts collection for The Sims 4 from the scratch. Some of the t-shirts works fine in game (both CAS Demo and full game) but some crashes the game when I hover a mouse pointer over it when I want to select it. I'm using the exactly same process for every shirt:
Make a base using Color Magic,
load a DDS template I've exported earlied in GIMP without mipmaps,
edit the t-shirt as I need it (paste an image on it, change a colour of it etc.),
export it as DDS with DXT 5 compression and generate mipmaps,
import the DDS to the t-shirt package and save it,
put it in my Mods folder.

This works for the most of them. But some just refuse to load its preview in CAS and make the game crash. I've even managed to show one of the non-functioning t-shirts on a randomly generated sim (who happened to load with the t-shirt on), but when I wanted to select the exact same t-shirt from the menu, the game crashed again.
Anyone knows why is this happening?

Moving to Create > CAS parts (Help is for help with the game). Sounds like you’re using a really old version of ColorMagic – see here for gory details.

Thank you. I've thought I have the latest version since I've downloaded it from the official page two days ago. I'll try to update it and post results.

Yeah there is an old download still up somewhere, unfortunately. I PMed granthes about it just now =). The correct link (the one that always has the current version) is id=404 -- easy to remember

Haha, yeah. I noticed it and giggled.
I tried to repair the faulty ones using the tutorial on the official EA The Sims forum, but when I want to confirm the changes, S4PE shows me an application exception message (but it's in czech so it won't be much of help; it's something about .net fx 4, but I have the newest version already, so it's weird). I've downloaded the newer version of CM and I'll try to import the DDS again.

So now it works. And I can even change the colour swatch now in ColorMagic, sweet. Thanks for your help!

Speaking of which, is there a way to change colour swatch AFTER I export the item using ColorMagic? (unless it's the resource with _IMG tag in S4PE, which isn't showing for me for the same reason I can't fix the faulty items, .net fx 4 exception)

There is a way – don't recall the steps off the top of my head, but that has come up before (it involves opening your package in CM and then doing .. something). Look in this forum or in Tools for other threads about it! I think I also put some links in the tutorials sticky in Tutorials.

You can also just open the package with s4pe, right-click the _IMG, click Replace, and replace it with your new swatch image. Your swatch should be a 32x32 DDS saved as DXT1 with no mipmaps.

It shows the same exception as before. But surprisingly, it actually works despite the exception. Anyone knows why it's showing for me, though? Or is it showing for everyone? (The red sentence in the brackets should be a translation of it.)

That error shows for everyone. s4pe is not yet able to read those images and display a preview, but it imports the image data just fine.