http://pastebin.com/ZHnMGFS3

OpenBlocks-1.7.10-1.3-snapshot-566

java.lang.NullPointerException: Rendering Block Entity
at openblocks.common.tileentity.TileEntityTank.getCornerFluidLevel(TileEntityTank.java:366)

Sanity check: do you have Optifine or Fastcraft installed? Logs suggest that you don't have them, but looks like some classes are ASMed (mismatched line numbers).

I think at the time of this crash I did not have fastcraft or sampler installed. I have been testing with them off and on, I am sorry.

Just got the same crash a few minutes ago. Running Optifine + Fastcraft

Can confirm these.
Any advise to fix?

What was the formation of your Tanks? ( How were they arranged? )
Did this occur on world/chunk load or immediately after you placed a tank?
Did you place it alone or did it have neighbours?

I have no idea what was causing TESR to render before validate() call (couldn't even find valid path in code), but I added null checks in b98fa28. Was keeping this issue to remind me to dig deeper.

Seames not fixed in the recent version.

Well, that's interesting, because this exact stacktrace is now simply impossible. If you can reproduce this error, please post crashlog.

http://www.dertobi.name/~tobias/upload/Minecraft/logs/OBTank/

Ok, something is doing weird things in there.

Can you describe what were you doing before crash? Have you moved tank with any other mods? I see ArchimedesShipsPlus on your list.

Nothing unnormal i think,
This concrete crash is from a player on my server, he has a large wall of Tanks filled fully with Water, and harvested a tank with a Tinkers Construct Pickaxe.

Ok, another try: fd467be (snapshot 587).