Error overview
This Salesforce error that Gearset is surfacing is usually encountered when deploying a Custom object that references a Visual Force page with the API name <xxx>.
An example of this validation error may look as below:
"<xxx> does not exist or is not a valid override for action <xxx>".
In this context <xxx> refers to a specific Visual Force page with the API name Application while <yyy> references an action View.
Resolution when you use 'Compare and deploy'
Workaround 1
To resolve this issue in Gearset's Compare and deploy, try adding Lightning page metadata to your metadata filter.
This should allow you to include the Lightning page that may be necessary in the deployment package for a validation to succeed.
Alternatively, you can use Gearset's pre-defined Default comparison metadata filter, as it also includes Lightning page metadata.
Workaround 2
Does your comparison results show that Custom object (e.g. YH_Application on below example) for which the error message is thrown depends on a new Lightning page component (e.g. application in below example)?
If so, this may be a reason why the deployment fails and Salesforce returns a validation error on Custom object metadata.
Explanation of the deployment logic Salesforce follows
Our understanding of this error message is also based on the Salesforce metadata API logic. What we mean by this is when deploying multiple metadata items the order of the deployment is important.
Imagine you have metadata A (Custom object YH_Application) depending on metadata B (Lightning page application).
If you deploy metadata A and B together in one deployment package, there is no guarantee that metadaa B will be deployed before A. Salesforce may choose to randomly deploy metadata A first. In that case A will fail because B is not there.
Gearset doesn't have the power to enforce on Salesforce the sequence in which the metadata components should or must be deployed, even if we know a specific deployment sequence may avoid a Salesforce error from being returned.
That's why often in such case the best solution is to split the deployment and deploy metadata B on its own, then deploy metadata A afterwards.
Alternative solution
Based on the information on the CannTechnology blog (Aug 2016) - a solution that worked for another user was to:
1. In the source org navigate to Lightning record page for the Custom object that error was thrown for.
2. Activate the record page and assign it to specific users, or assign it as an org default.
Further examples of this Salesforce validation error and guidelines on how to resolve it can be found in below resources:
Trailblazer Community post (Jun 2022) with a reference to solution proposed on Salesforce StackExchange forum (Oct 2014)
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.