SC500 series cards can either use box headers or angled header pins for the bus connector.
Angled header pins are low-cost but are very easy to insert out of position.
Box headers are more expensive but protect the pins as well as help align the plug.
While the box headers help with alignment they are not perfect. They are designed to mate with a ribbon cable which is a bit longer than the PCB mounted sockets used on the backplanes. As a result, it is possible to fit them out of position.
To prevent this you can glue a jumper shunt inside each end of the box header, as shown below.
Make sure they are glued tight against the end of the box header or the header will not fit over the socket. Superglue works well but don’t get it on your hands! Also, make sure it is completely dry before connecting to a backplane.