I've found other posts where people lists the same cards and have them working and the Sandisk card also work with the pcmcia adapter so it should work with the cf adapter too?
Some CF cards can be configured to be removable/non removable, PC's won't boot from them when it's set to removable. I don't know if that affects Amiga's.
It could be the cable. I had to replace the one in my A1200 when it started only working sometimes. Also if the cable isn't key'd then make sure you have it plugged the right way round.