The block size of the specified redo log file is not valid. The file might not be a log file, or it might be a corrupted log file. In an Oracle RAC environment, this message includes the name of the relevant RAC member.
The PowerExchange Express CDC for Oracle log reader tries to use the alternate log file that has the same sequence number. If this alternate log file does not exist, CDC processing ends.
Restore the log file, or if you cannot restore the log file, rematerialize the target. Then cold start the CDC session.