Edit: Oops, posted in the wrong window... Oh well, this is good advice anyways.
Use GtkRadiant, it's a far superior editor, much more stable, fast, easier to use, and is updated often. It also comes with an incredible compiler that makes your maps look better, run faster and compile much faster.
http://qeradiant.com
The newest stable version is 1.2.11, with the 1.2.13 update.