Snapshot Multisite Blog Backup

Hi Guys
I have read the other support questions but can't seem to find the answer to my question. I understand to backup a multisite that you must add a new snapshot for each site. To do this you change the Blog to backup by using lookup. But this is where I get stuck.

My backup worked for the primary site:

But when I want to create another snapshot of my other site 309 it throws an error: Error on blog lookup. Try again.
I have many sites on this multisite and have tried many and I get the same error. This is the one I'm trying to backup:

Any help would be awesome. Thanks