Hi Marco,
See this page for notes about changes to skinning. Built in skins should work fine. styleshout-coolwater works fine here and on my sites. I've seen some strange things with svn lately where it doesn't always get all the files by svn update on root folder. You might try svn update on the Data folder/
There are some new files in the skin folders, but csshandler.ashx is not one of them.
The url is not incorrect, the csshandler.ashx does not have to really be in the skin folder because of a httpHandler web.config setting:
<add verb="*" path="*csshandler.ashx" type="mojoPortal.Web.UI.CssHandler, mojoPortal.Web"/>
In fact there is no file named csshandler.ashx, it comes from Web/Components/CssHandler.cs
Hope it helps,
Joe