Uncorrectable PCI Express Error on DL380G6

This server has been randomly crashing. Sometimes the boot halts, or it crashes the OS after a while.
This is an entry in the IML: Uncorrectable PCI Express Error (Embedded device, Bus 0, Device 8, Function 0, Error status 0x00000020)
According to lspci, this is on bus 0 device 8: 00:08.0 PCI bridge: Intel Corporation 5520/5500/X58 I/O Hub PCI Express Root Port 8 (rev 13)

Does anyone know what might be causing this? Is something on the mainboard dead? Or could it be one of the PCI cards?