As a matter of fact this might be a compatibility problem due to the fact that most of these devices are tested and certified for server platforms, not desktop computers.
You may troubleshoot the issue testing another card (a regular one, as a wireless LAN card, a simple video card, etc.) to check that the port itself is working fine. Update the BIOS of the system you are using and in the other hand update the firmware of the card that you are having issues with.
Furthermore, check with the card manufacturer to see if the card has known compatibility issues with this motherboard or if this would be certified/qualified to work in this system.
For a list of tested components for these parts you can refer to:
http://www.intel.com/support/motherboards/desktop/sb/CS-033293.htm Desktop Boards | Thin mini-ITX component catalog
Reply from Adaptec:
According to the information in our database, you seem to have an OEM controller. We do not support OEM products because of their specific and for us unknown configuration. Please, turn to the OEM manufacturer to proceed with the troubleshooting.
If this wouldn't be an OEM controller, I would suggest to update the BIOS of the controller and also the BIOS of the mainboard. Then insert it in a different mainboard and disable the "SCSI Int 13 Support" option. For more on this, please, refer to the following ASK article: http://ask.adaptec.com/app/answers/detail/a_id/2353/ http://ask.adaptec.com/app/answers/detail/a_id/2353/.
The newest BIOS of the mainboard is available for download here: https://downloadcenter.intel.com/SearchResult.aspx?lang=deu&ProductFamily=PC-Mainboards&ProductLine=... https://downloadcenter.intel.com/SearchResult.aspx?lang=deu&ProductFamily=PC-Mainboards&ProductLine=....
Additionally simply try to run the controller in a different mainboard. The Intel DN2800MT is a desktop level mainboard with a very limited connectivity in terms of PCIe.
That seem to point also to the lack of compatibility between that add-in card and desktop platforms, specially if they are indicating that you may be using an OEM product, which should be only installed and configured by an OEM. At this point, you may follow their recommendations to see if it works. Otherwise, you may need to check for another model, checking with its respective manufacturer for compatibility tests before installing the card.