i know this is a late response but... I've been fighting this thing for 2 weeks and figured i'd post what worked for me. just started playing around with mining. I have a dell t5400 and t7500. I purchased a rx 460 and ran into the same issue with error code 43 tried with existing win10 pro x64, updating to latest bios, ran into error so i performed a clean install... same issue. Installed win7 pro 32 & 64... same issue. Installed ubuntu 15.10... wouldn't detect properly . Tested in every full pcie slot i have. Installed card in main rig (i7 6700k, z170, etc...) worked perfectly. Figured these workstation boards were made for quadro cards since the card was confirmed good so i returned the card. Went a week looking at pc parts for a new build just for eth mining because i really wanted to run the new rx cards due to performance and eff in mining, not to mention price. Ran across this forum and figured id take the risk again. Purchased a rx 470 this time... popped it in and same issue. I then installed an old gt 520 in pci-e slot 1 and the rx 480 in slot 2. BAM... card detected, drivers installed properly and working well. decided I test and pulled the old gt 520 out and see what happens. Booted the t7500 and everything is golden. Only issue is you cant configure bios with the amd card. work around is to have an old spare nvidia card around if you need to make changes in the bios. This also applies to the t5400.

I wanted to post my experience to hopefully help anyone who runs into this issue like i did.