This article discusses the Unknown User Permission metadata deployment error that you might have received.
This error is typically received when you are trying to migrate metadata from a sandbox to another sandbox or to a production Org. Salesforce introduces new functionality 3 times a year. Additionally, you can turn on and off features with or without salesforce's help. These actions could trigger an introduction of additional user privileges.
The issue is that these user permissions are not propagated through all the sandboxes or production Org(s) until the salesforce release schedule catches up or if you turn on/ off appropriate feature set on the destination as well.
The easiest way to handle this is using the Remove References feature in Deploy Assets dialog's Deploy Assets tab. Remove References, when selected, will automatically remove unknown metadata automatically from Profiles, Permission Sets, Page Layouts and Custom Objects. You can further add any strings to the Remove References list and these references will be automatically removed (see attached).
Pro tip: You can add asterisk (*) to the beginning and end of the string to create wildcarded strings.