It means that none of your compute hosts has sufficient resources to run the instance, or the right architecture, or other properties imposed by the flavor and the image metadata. You may find details in the log files for the placement service and the nova-scheduler, in particular if debug loggin is enabled.

A common problem is unability of compute nodes to register with the Placement service. Run the command nova-status upgrade check to see if this is the case.

use opwnstack host show HOSTNAME to see free resource of node. if every thing ok restart service in compute