I have problem with installing NetBeans Plugin Development.
I have tried turning SDK off and on, and try again, but again this message appeared.
I haven’t seen that error before. What version of netbeans are you using? If v8, try using v7 instead. Uninstalling and clearing out your netbeans user directory too, can often help with these issues.
I used v7 and everything is fine now. 
Excellent =)
v8 is pretty new and all the plugins need to catch up