We are developing a system where we have to control 14 PCI-Cards. We are currently using the OSS-PCIe-4U-EXP-2022-x8-850 system and a PC with the X8SIA-F mainboard from Supermicro. The System starts fine with 7 or less cards in the expansion kit, if I have more cards in the PCIE-expansion chassis the computer does not boot. We did a bios update and everything but it just doesn't want to boot. Do you have any ideas how to solve this problem?

This type of issue is almost always BIOS related. Either the BIOS does not have enough device numbers available to handle more than the 7 you are plugging in or it does not assign enough memory for Memory Mapped IO (MMIO). If your BIOS has the options available in it, you can try assigning MMIO to space above 4GB and increasing the amount of memory assigned. If these option are not available in you BIOS then the only resolution is a change to the BIOS by the manufacturer.