3 of 4 thruster packs experienced the issue; they need 2 of 4 to open the solar panels and 3 of 4 to dock with the ISS. From what I understand they got all 4 working again using the "water hammer" effect to clear the blockage, but I'm not sure how accurate that is.
Imagine it's your job to fiddle around remotely with fuel pump electronics (or whatever may create that water hammer) within a time window of maybe 20 minutes or else you've just sunk a 100M investment somewhere in the ocean. Must be lots of fun o.O
I remember it being something about check valves in the oxidizer pressurization system. I don't recall where I read that, but it's probably not too hard to dig up (I'm just lazy).
