Explanation of the error:
This error is surfaced by Salesforce when trying to relate or deploy directly to an object that you don't have permissions to access.
Resolution:
Check the permissions on the object you are trying to relate or deploy to, and grant permissions on the objects for the user you are deploying as.
Further examples of this Salesforce validation error can be found here:
Disclaimer: This error is returned by Salesforce directly, rather than Gearset. Even so, we offer guidance based on our combined experience with the Metadata API. Where possible, we try to help guide you to fix or avoid this error. In the case that this isn't possible, we may need to direct you to Salesforce support for further clarification.