I can no longer get Dev Mode to launch. I feel like I've tried everything. Verified/reacquired files. Switched back and forth to/from v1111 and v1112. Made sure Force 32 bit was unchecked. Disabled my firewall. Uninstalled/reinstalled game. I can't get a trace, because it just flashes right back to launcher (or at least I can't find a trace file).
I had the same problem. Try deleting, or moving to different location (Desktop) the UserData folder found in the ModDev folder. \Steam\steamapps\common\rFactor 2\ModDev\UserData
I think I fixed it before reading your post, but thank you very much for responding. I went to the BIN32 folder (which I thought we were to delete a long time ago) and launched the DEV exe from there. It worked. I went back to BIN64 and tried that exe (which was not working) and it worked. Button in launcher works now as well. Crazy game...
I had the same problem. I tried all of the above suggestions and nothing worked. I think the XINPUT_3.dll DirectX file was corrupt. Reinstalled DirectX and it fixed the problem.