Where did you find those directions? Those are for installation from zip archives, for people doing offline installation...not from the Eclipse Update Manager (which is what you did). There is no SlickEditCoreSetup directory in your case.
Anyways, to get the plug-in up and running, if you downloaded/installed via the Update Manager, all you have to do is restart Eclipse, like it will tell you to do after the install. The chmod step was already taken care of automatically during the installation. Then when Eclipse restarts and you go to activate something from SlickEdit in Eclipse...the licensing process will begin, and it will walk you through it.
It looks like your installation should still be fine...what distro are you running, and what Java version/vendor are you using? Is Eclipse or your Java 64 bit? Was the Eclipse installation installed with your system or did you actually install it from eclipse.org? To run the plug-in on Linux you need 32-bit Java from Sun version 1.5 or later. You also need to make sure you have libXp installed on your system (capital X).
If all this checks out, and you are still getting the error, run eclipse like this: eclipse -vstrace. Then try to activate something from SlickEdit. You will get some debug output in the console...copy that output and either attach it here as a txt file, or if you would rather you can send it into support@slickedit.com and reference this thread.
- Ryan