Eclipse editor won't open

Question

My Eclipse cannot show the editor window.

Error:

Could not open the editor: The editor class could not be instantiated. This

Answer 1

I was getting this for FlashBuilder 4.7. It was a permissions issue. On Mac OSX, from the info box, I gave my user READ & WRITE access to Flash Builder 4.7 folder, then did "Apply to enclosed items..." and that fixed it.