Posted by gouessej on Mar 28, 2012; 8:42am
URL: https://forum.jogamp.org/Problem-when-using-an-external-context-tp3851637p3863930.html

The explanation is here:
http://msdn.microsoft.com/en-us/library/dd374383%28v=vs.85%29.aspx

If the calling thread has a current OpenGL rendering context, wglGetCurrentContext returns a handle to that rendering context. Otherwise, the return value is NULL.

Maybe the context is not current when you try to create an external context. Be aware that the context becomes available later in JOGL 2 than in JOGL 1 but it concerns the Java side.