ORA-64781
Section string of the prior multi-section backup set string of data file string is missing.
Cause
A section of the previous multi-section backup prior to the current backup was missing. Without the section, INDEX_BACKUP tasks for processing the current backup set remain in ORDERING_WAIT state.
Action
An INCREMENTAL LEVEL 1 CUMULATIVE or INCREMENTAL LEVEL 0 backup of the data file should clear this condition.