The answers finally came out, and say a lot about modern warfare. First, the C-802 missile that hit the helicopter hanger on the Israeli ship suffered from a common problem with missiles. The warhead failed to go off. The fire on the Israeli ship was caused by the half a ton of missile crashing into it, and unburned rocket fuel. The other C-802 fired, homed in on a nearby Egyptian ship, and sank it (the warhead on that one did detonate). The Israeli anti-missile system was not turned on because it was found to interfere with the electronics on Israeli warplanes operating in the vicinity. This is also an increasing problem in modern warfare. There are so many electronic gadgets transmitting, that there are more cases of signals, literally, getting crossed.
The C-802 is a 20 foot long, 360mm, 1,500 pound missile with a 360 pound warhead. The Israeli warship carries electronic defenses against anti-ship missiles, as well as a Phalanx auto-cannon. This systems is supposed to be turned on whenever the ship is likely to have an anti-ship missile fired at it. The Phalanx radar can spot incoming missiles out to about 5,000 meters, and the 20mm cannon is effective out to about 2,000 meters. With incoming missiles moving a 250 meters a second, you can see why Phalanx is set to automatic. There's not much time for human intervention.
The C-802 needs to work with a radar that can track the target. The C-802 apparently used Lebanese government coastal radars for this. The Israelis destroyed those radars after their ship was hit, and no more C-802s were fired. The C-802 is 30 year old technology, and Iranian quality control in its weapons plants is known to be uneven.
The use of two Iranian C-802 anti-ship missiles against an Israeli warship on July 14th, left some unanswered questions in its wake. For one thing, why wasn't the 1,100 ton Israeli corvette destroyed by the 360 pound warhead of the C-802? And why weren't the ships anti-missile defenses turned on?