"cannot resolve gap for one or more standby databases"
*Cause: The primary database could not resolve a gap request from one or
more standby databases.
*Action: To see which standby database has an unresolvable gap, check the
status of the primary database using either Enterprise Manager or
the DGMGRL CLI SHOW DATABASE command. Copy the missing archived
log files from either backups or from another database in the
configuration that has the files to the standby database that is
missing the files.