Error:
Could not open the editor: The editor class could not be instantiated. This
Google this error and you get plenty of hits in a variety of (Eclipse) IDE's and plugins. There seems to be no record of real 'fix' though, besides the one you found out where you create a new workspace.
3.6.2.r362_v20110210 is the version I'm running. Are you sure you're on 3.6.2? You're first edit lists
-startup plugins/org.eclipse.equinox.launcher_1.1.1.R36x_v20101122_1400.jar --launcher.library plugins/org.eclipse.equinox.launcher.win32.win32.x86_1.1.2.R36x_v20101222
which seems to point at an older release.
I agree with another poster that you should definitely search and/or post this on Eclipse's bugtracking system. That's the least you can do when you use open source software.