HW Error on Nth(Last) GPU

[eddaviking]

Hi, I've recently added 2 more GPUs to my rig which is now 4 using PCIE risers.  My problem is I am getting HW errors on my last GPU example 4th GPU when all are installed.  If I remove/disable the 4th GPU, I get HW errors on the 3rd and so on and so forth, always getting HW errors on the last GPU while the rest are ok.  Anyone knows why this happens.  I tried lowering the intensity of the last GPU but this also lowers the kh/s.  I do have 4 identical Sapphire r9 dual x. Windows 7 64. and using the latest drivers. This happens running CGMiner/SGMiner. Thanks.