I got that same error awhile ago. Here is a tutorial of forge gradle .965: http://www.minecraftforge.net/forum/index.php?topic=14048.0. Before you do the instructions uninstall java 8. Then once you did what it told you to do, it's sorta like .964 but it's forge gradle. For you workspace in eclipse, make sure you clicked eclipse, if you know what I mean.