Verbatim from the article itself:
But two major issues worry Ebersole.
“I worry about software development — meeting the incremental block deliveries, and the other key one right now is the helmet,” he said.
Thereafter the Navy source was introduced to qualify the concern Ebersole raised about the ability to deliver software to future incremental blocks, like Block 4.
http://www.defensenews.com/article/20120224/DEFREG02/302240004/JSF-Chief-Engineer-F-35-Military-Flight-Release-Happen-Soon[/b]