Some Domains Cannot be Manually Migrated

[flyingcork]

Hello,
I'm using the Migration and Transfer Manager to move domains and accounts from a server running Plesk v10.4.4_build1013120126.11 os_CentOS 5 and I'm moving to a server running v11.5.30_build115130819.13 os_CentOS 5. I did a full migration with no errors, but I'd like to be able to move "Only manually selected resellers, customers and domains" in order to get specific domains up to date. The problem is that several domains simply do not show up in the list of potential domains to be transferred. What could cause this? How can I move these specific sites?

Thanks