ORA-19648: datafile string: incremental-start SCN equals checkpoint SCN
Cause: The incremental-start SCN which was specified when starting an incremental datafile backup is equal to the datafile's checkpoint SCN. Since an incremental backup can only be applied to a datafile whose checkpoint SCN is between the backup set incremental-start SCN (inclusive) and the backup set checkpoint SCN (exclusive), there is no datafile that this backup set could ever be applied to
Action: Specify a smaller incremental-start SCN. NOTE that this message will usually only be encountered by the user while taking an incremental backup with Recovery Manager. Recovery Manager should intercept all usual cases of this error and simply ignore the incremental backup for this file. So, if you do encounter this error, please report it to Oracle Support
https://support.oracle.com/
http://www.oracle.com/