You may see this Salesforce validation message when you try to deploy a Workflow, where one org is Enterprise and the other is Professional.

Workflows are only available in Enterprise level orgs and upwards unless purchased from Salesforce as an add-on to a Professional org.

This error occurs because we are trying to query Salesforce for a type of metadata that is not supported. You can get past this by removing the 'Workflow' metadata type from the metadata filter and then re-running the comparison.