Running into a frustrating issue right now.  I finally got the entire loop built for the Black Box, and low and behold while leak testing, there was a leak... the culprit?  the recess for the O-Ring broke.  See here:
 

 
So, I fix that, and move on.  When I reinstall everything, I get a blockage somewhere and I don't know where or HOW.  Where ever it is, the Bitspower fittings are leaking from the inside where the tubing is, see here:
 

 
This is the full loop:
 

 
Prior to the stupid terminal issue, there loop passed through 100% back to the res, but had a minor leak where the terminal was open. After fixing, the water gets stuck somewhere.. I have NO idea what is going on.  If I take the return line off the res, the fluids flow all the way through the loop when I create a vacuum.  
 
In the last picture, this was after redraining the loop for the 3rd time.  Next step is to remove all of the GPU's again..  Any ideas?
 
 

I would hope not.  I will tear it all apart tomorrow. I am too frustrated to try tonight.

Check the pump, as it could be faulty. If the pump is not keeping the right pressure, it can appear to be a blockage since the flow would just stop at a certain point. Given the number of items in your loop, the orientation and distance the coolant needs to travel, the pump will need to be at maximum rpm to get the flow necessary. Pressure test the pump before tearing everything down. When you rebuild a loop, it can take a bit longer for it fill, as the pump will need to pressurize the loop. Turning the pump off and on can help it to get the pressure back where it needs to be. This has happened to me before. I was impatient and rebuilt the loop several times only to find nothing. When I realized that and just continued to work the pump, it filled and got the pressure necessary, but it took time.

I have a EVGA x10 mouse
I think there is something interfering with the sensor
and the sensor is not accessed for users to fix
what should I do? 

Emil sune
I have a EVGA x10 mouse
I think there is something interfering with the sensor
and the sensor is not accessed for users to fix
what should I do? 

I will post on your mouse question itself, so this topic stays on topic.  A mouse issue is very much different than a leaking system, lol.

Here is what you can do if the O-ring is too recessed:
 
1: make a new O-ring - make it longer so that the material will bunch up more and have a same function as being thicker (i can help you with that if you need)
 
2: lower surface - since its plastic you can get sandpaper on a flat surface and sand away until the O-ring stands up taller
 
3: return the block - depends on the makers warranty and how desperate you are to get up and running 
 
3: last by not least...PERMATEX

O-rings can get damaged when taking the loop apart. Even the ones that are double need care. I can be a bull in the china shop, as I have done that many times. Taking apart a loop and re-installing everything is a daunting task. I would also make sure all screws are tight. Might have one or two that are not. As the pressure builds, the ones in various states of not being tight, leak. Seems random, but when pressure is too much for the tightness of the item it exposes a leak. Nice to hear EK is doing things to help.

Scarlet-Tech
I fixed the block leaking.  It is the Bitspower fittings.  I am pulling them off now, but the fittings themselves have started leaking, so I am going to pull all of them and check the O-ring.  The issue I can't figure out, is that every one of them are double seal o-ring like this:
 
  So far, at least 3 fittings have randomly leaked... and I don't know why.

Yeah, I'd double check the o-rings and also the tubing to maybe deburr or sand the edges. It might be that a rough spot is stopping it from making a good seal. I've had that happen before, but it didn't create a large leak. 

O-rings and fittings are temperamental. You may not be able to see the issue. Even if the damage is not visible, does not mean that when the loop is under pressure it will not fail. Replace the the fittings may be the best option, unfortunately. I always buy many more fitting than I need just in case. Could be the rings in the screw part that seals the fitting to the water block. The pressure exposes all potential problems.

Step away from the rig. Go to the refrigerator. Take out a beer. Drink it. Do this over and over until the thought of water loop leaks leaves your mind. Repeat again tomorrow. Enjoy part of your weekend, as it is a tribute to your selfless service to our country. We appreciate it. After the weekend, come back to the project with a clear and hung over mind. It will help you to solve the problem. I guarantee it!

Have you thought of using an EK-FC Terminal QUAD Semi-Parallel Block?
 
I have used mine with various EVGA Graphics Cards in 4-Way SLI under High Pressure/Flow Chilled Water Cooling with Great Success.
 
Unfortunately I originally bought mine from Frozencpu.com., Which I believe is no longer in business(?), But EK still has them.
 
Sorry about the Long Description Link, But look at page 2.......
 
http://search.isp.netscape.com/nsisp/boomframe.jsp?query=ek+serial-parallel+water+block+connector&page=1&offset=0&result_url=redir%3Fsrc%3Dwebsearch%26requestId%3Dab7ab72ba908a0b1%26clickedItemRank%3D2%26userQuery%3Dek%2Bserial-parallel%2Bwater%2Bblock%2Bconnector%26clickedItemURN%3Dhttp%253A%252F%252Fwww.ekwb.com%252Fshop%252Fblocks%252Fvga-blocks%252Fmultiple-block-connectivity%252Ffc-terminals.html%26invocationType%3D-%26fromPage%3DNSISPTop%26amp%3BampTest%3D1&remove_url=http%3A%2F%2Fwww.ekwb.com%2Fshop%2Fblocks%2Fvga-blocks%2Fmultiple-block-connectivity%2Ffc-terminals.html
 
 
EDIT:
NCIXUS has ONE Left in Stock.... EK-FC Terminal QUAD Semi-Parallel
 
http://search.isp.netscape.com/nsisp/boomframe.jsp?query=EK-FC+Terminal+QUAD+Semi-Parallel&page=1&offset=0&result_url=redir%3Fsrc%3Dwebsearch%26requestId%3Dab7ab72ba908a2c2%26clickedItemRank%3D15%26userQuery%3DEK-FC%2BTerminal%2BQUAD%2BSemi-Parallel%26clickedItemURN%3Dhttp%253A%252F%252Fwww.ncixus.com%252Fproducts%252F%253Fminorcatid%253D1165%26invocationType%3D-%26fromPage%3DNSISPTop%26amp%3BampTest%3D1&remove_url=http%3A%2F%2Fwww.ncixus.com%2Fproducts%2F%253Fminorcatid%253D1165
 
 
There is also one on FleaBay.....
 
http://www.ebay.com/itm/EK-FC-Terminal-Quad-Semi-Parallel-/201355085630?pt=LH_DefaultDomain_0&hash=item2ee1b2c73e

Someone, please tell me when the punch line will hit... this joke has been going all freaking day, and most of last night.
 

 
before the question comes out, yes, I tested the one throwing the error before all of this.  Nothing changed, yet here we are.  The one card that didn't have any leaks near it... 

 
I don't know if you have all the Vbios switches on the four cards set at "norm" or "LN2", But switch them to the opposite position they are in and see if you still get the same error.
 
You could also try to lift the cards slightly out of the PCIe slots and try to re-seat them, although this unfortunately MAY cause a leak to appear again.

I just used pictures from my ReTIM thread to verify if all of the PCB components were intact.. :-D  

I removed the fittings complete, went from Semi Parallel to Series only.  Going to order the appropriate bitspower 16mm tubing and see if that works.  Right now I am using Monsoon 5/8" and that may be the issue, so I will need to get the other tube in to test and give a definitive answer.