After changing the compression and deduplication settings for an existing backup job to be more aggressive, (which I detailed in my previous post)  I ran into the following problem ‘Source backup file has different block size’.

By changing the deduplication setting I have altered the block size of the very next active full backup file created. This appears to have upset my backup copy job which used the backup job as a source. After selecting an ‘Active Full’ on my failing backup copy job it resolved the problem.