CML Sometimes does that; stop and start device again; make sure image Dvd is attached and on.
Make sure device is fully booted; and make sure you have enough resources to run topo. I see you have Nexus switches, if those are 64-bit, they take lots of resources! CPU or RAM that could be your issue. what are your PC specs?
also see https://developer.cisco.com/docs/modeling-labs/#!faq/faq---cisco-modeling-labs-v2x
Regards, ML
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