I had an issue with this once and it ended up being a mis-configuration of my Location Bandwidth Groups. If you have the Location Bandwidth Manager Service activated in Serviceability, then CUCM will monitor network metrics to determine if a call is possible based on the setting provided for the location that the phones belong to.
You can test this by disabling this service to see if the error goes away. If it does, then you need to take a closer look at the settings for Locations that are participating in Bandwidth Management.
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