[SalesForce] Missing Organization Feature: NetworksEnabledOnce

If the custom object's name is Event__c, then yes, SF can get "confused" with the API name. You can log a case to get more details, but if you change the API name you might be able fix this. Give it a try.

This might be an issue because you might have added D&B fields in your package for account or contact records .

If your package is not managed released you can get rid off this fields from the package .I would get away these fields from the development org and get rid of dependency

Additionally double check these boxes are unchecked

Also check if you have included the fields in the page layout or any other metadata .Using an eclipse IDE would be helpful to pull package metadata and run a search against it