According to Metalink Note : 300989.1, when block change tracking enabled and using direct load operations, it is like to get an ORA-19694 on Oracle 10.0.1.x version specific to all the platforms due to a bug 4200702.
RMAN-569: =============== ERROR MESSAGE STACK FOLLOWS =============== RMAN-571: ========================================================== RMAN-3009: failure of backup command on ORA_DISK_1 channel at 02/14/2005 ORA-19694: some changed blocks were not found in the change tracking file
Workaround would be disabling change tracking feature.
According to the note, this is fixed in a patchset 10.1.0.5 and one-off patches are available for 10.1.0.4 and 10.1.0.3.
I guess, who are on 10gR2 and enabled the BCT feature doesn’t have this bug.