Depending on the type and amount of nodes you have in your topology, will dictate how much resources are required to run a simulation. Please refer to the VIRL Resource Calculator to get a estimate on how much memory and cpu are required: https://learningnetworkstore.cisco.com/virlfaq/calculator
The error message you received states not having enough resources to run your simulation. Check to see if you have any other running simulations that can be shutdown by logging onto User Workspace Manager (UWM).
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