I’ve been using the free version of Aptana on Windows for more than a year now however when I switched to Windows Vista 64bit the CSS view stopped working displaying only a black box as shown below.
Aptana Studio CSS Problem on Windows Vista 64bit
Although this bug exists since the end of 2007 it has only recently been fixed by the developers of Aptana.
The only solution to fix this problem right now is to download the alpha version of the upcoming release 1.4.
If you do not want to install an alpha version of the software you have to wait until the final version will be released or you will simply have to live with the fact. A simple workaround is to right-click on a CSS file and select to edit it with the text editor. Although you will lose all cool features like autocompletion and so on you can edit the CSS file.
An even simpler workaround is to click on one of the browser preview tabs (you can create them if you don’t have them already) and to come back to the code editing view.
This doesn’t work on my system - depends obviously on the Aptana version you are using - the workaround you are suggesting doesn’t appear to work on newer Aptana versions.