I just had the same problem. To fix it I tried typing gpuDX11.dll in demul.ini since the video plugin field was empty. Then trying to configure the video plugin wouldn't work, giving me an error message telling me that a dx9.dll was missing. So I tried to reinstall directX 11 and it did the trick, it works now. This fix comes late I know but maybe if it doesn't help you it will help others. Cheers guys!
Yeah but the problem with all of this is: You shouldn't have to go through all this mess.
Go back to older versions of Demul, the further you go back, the easier it finds the plugins. I know people are going to get ****** at me for saying this but be serious, it should not have to be THIS much of a hassle to make the most basic functions work. I get the whole bug issue thing, but locating files? C'mon....
I've been seeing all these posts about "reinstall" Demul. Reinstall? How? It unpacks to an executable. The best you can do is delete the config files or maybe wipe the registry listings with something like CCleaner. Also, i've seen posts about "reinstall" DirectX or C++ Libraries.....again, WHY? You don't have to do it with the majority of the other emulators.
Final answer, the problem is within the programming of the emulator.
I'll probably get raked over the coals for saying it or thrown out but being right about something does come with a price sometimes.
I will give a hint however: There really DOES need to be an "installer" that installs necessary files and cleans up certain activities so the end-user doesn't have to go to any of this work. It should also include an "uninstaller" that cleans up the mess before a new install is put in.