Guys, this is not a DLNA issue. DQSpot is playing from a PC running MC Server to a PC running a MC Client. While using JRiver Media Network does use some DLNA functionality, for discovery and such as I understand it, the playback part is not standard DLNA.
I suspect that if an ISO contained just an MP4 file, the Client would play it.
The problem most likely is that the ISO contains a Blu-ray rip. A MC Client won't play a Blu-ray folders rip, unless the Client can see the folder structure as a local file, so I don't think it will play a Blu-ray ISO either. But I don't have any ISOs to test with, and that is not on my agenda for today.
EDIT: Darky if it works for you, are you using a NAS with a common drive letter assigned for each the MC Server and PC Client? Otherwise, I would not expect what you said to work.
Note that MC will play a DVD folder rip from a Server to a Client, but only play the main movie, and not the DVD Menu. So someone could test playing a DVD ISO to check how that works... or not.
Anyway, DQSpot, see setting "Options > Media Network > Client Options... > Play local file if one that matches server file is found". Search the forum for that. See if you can set up the conditions that allow that setting to work. i.e. The server sees the file as Z:\Movies\Crackers.iso, and the Client sees exactly the same path and filename.