Dragon2 has two thrust systems - Draco, which is responsible for maneuvering in orbit, and SuperDraco, which is only used to escape from an exploding Falcon 9 (because one exploded before and they want to be safe). The explosion happened during a SuperDraco test. Now, these SuperDraco thrusters had been tested on land before, and they were fine, so there's *speculation* that it's related to saltwater damage. But we don't know. And until NASA knows - and then, until the American people know - Dragon2 is grounded. As is appropriate. I don't know that getting into the tanks would have ever been an issue, but I haven't had to deal with hydrazine and saltwater before. There's a lot of speculation and I think it's safest to say we just don't know.

If it's just an issue with SuperDraco being exposed to saltwater, SpaceX might get back to flying pretty soon, because SpaceX has promised a new capsule for every Crew Dragon flight. But it might make it harder for SpaceX to *bid on future cargo missions; they were planning to use used Crew Dragons as cargo Dragon flights. Cargo Dragon doesn't use SuperDracos, but the safety protocols might be an issue for NASA.

Hope that answers your questions!

As an edit, it might have been an over-pressurization in the SuperDraco fueling system, but we don't know yet. They're still gathering debris from the landing zone where they were testing it. I think it's a really good question and I think the investigation will reveal more.