Enable debug mode and look in both the console and the network trace (I'm assuming this is an ajax request). You could also search for the phrase and edit the file (not highly recommended) to log certain data whenever it's called.
Enable debug mode and look in both the console and the network trace (I'm assuming this is an ajax request). You could also search for the phrase and edit the file (not highly recommended) to log certain data whenever it's called.
When it's happening, you can enable debug mode to get a more specific error. But normally something would be logged in the control panel for this sort of error.