Hey, I just downgraded from openjdk 7 to openjdk 6, thinking that everything would work as normal, I opened up the SDK and found that I couldnt build my project. Must I upgrade again or is there some kind of backwards compatibility?
No you should be able to build, unless you used java7 features.
But it is really impossible to tell since you give no information: What do you mean couldn’t build? Error messages? Logs? How do you mean downgrade - Installed JDK6 also? How? Did you set up your environment correctly? What OS are you using? Did you try to build a new project (i.e. does your environment work at all)?