The feature class used as the reference data may not be accessible because of the following:
- The feature class is stored in a remote folder or on an external disk drive.
- The primary reference data is a feature service on a server with low performance or network latency.
- The primary reference data is a feature service and the internet connection to the server is lost.
- The feature class is locked by another user.
Ensure that the data source is available, and build the locator again.