This has happened several times, most recently with a theme called PlanB, from:
http://www.wincustomize.com/explore/winstep/218

I used Themes:Import, Winstep *says* it imported the theme, but it does not show up in the list... is there a maximum number of themes in the list?? Or am I doing something wrong?

There is no maximum number of themes.

I don't have time now to check that particular theme, maybe it's missing a vital configuration file?

Also, remember that a theme made *only* for NextSTART, for instance, will NOT show up on WorkShelf's list of available themes.

hmmm... interesting... how would I know if a skin is NextStart only, rather than a full Winstep skin? It doesn't have a .xtreme file, but the zip file *does* have .wsc, .wsr, .wst, .wsw ... which is comparable with other zip-distributed themes that *did* show up successfully.

.wst is the NextSTART configuration file, .wsw is the WorkShelf configuration file.

Check to see if the theme was properly imported into C:\Users\Public\Documents\WinStep\Themes\

Interesting... no, it was not there... I extracted the theme into that Themes directory, and it immediately popped up in the Preferences:Themes list.

I wonder if the theme has a bug of some sort in it?? Although the theme now shows in the list, it does not actually render properly... Active processes all pop up in a button bar in the middle-bottom of screen, but task bar is not present. Also, the... ummm... bar that shows "main, desktop, recent, etc" is stuck to bottom of screen. (sorry I don't have the Winstep terminology down yet, program is still new to me!!)

I've seen this before on another theme, though I can't find it at the moment... I suspect these are older themes that aren't following some rule of current version.

Wow, that is an oldie but goldie. From 2002. It's possible that it needs to be updated to current standards, but Jorge would know better than I. Plus there are quite a few skinners who see these posts (I hope they are still out there)