Warning: It is likely that your modifications to will result in a view that cannot be indexed. Click CANCEL to discard your ...

Warning:  It is likely that your modifications to <0s> will result in a view that cannot be indexed.   Click CANCEL to discard your modifications and preserve the existing view and its indexes.   Click OK to discard the existing indexes and alter the view.  SQL Server will reestablish  the indexes only if it determines that the altered view can accommodate indexes.