Dell PowerEdge 2950 PCIe Training Error — No PCIe cards inside

So I recently found myself an old PowerEdge 2950, and when I turned it on (after me almost having a heart attack by the sound of it starting up), during post it halted with an error of PCIe Training Error : Internal PCIe Card. The weird thing there, is that there aren't any PCIe cards in the 3 slots. The rightmost (bottom, in the picture) slot however, seems to come out of the board as an expansion of some sort? Could that be a problem? In case I'm missing something really obvious, I've included a shot of the whole system.