The solution '%s' has been modified outside the environment, and there are unsaved changes to the solution. Press Save As ...

The solution '%s' has been modified outside the environment, and there are unsaved changes to the solution.

Press Save As to save the unsaved changes and load the updated solution from disk.
Press Discard to discard the unsaved changes and load the updated solution from disk.
Press Overwrite to overwrite the external changes with your changes.
Press Ignore to ignore the external changes. Your changes may be lost if you close and reopen the solution.