Account cannot be removed (Automatically Set Permissions)

As Gabe informed, automatic permission cannot be remove from archive manually via VAC by simply deleting it. You need to simply zap the permission by running EVPM script

Open notepad, save this file with '.ini' extension and encoding must be 'unicode'. Put following content.

[Directory]
DirectoryComputerName=kvsvault
SiteName=archivesite

[ArchivePermissions]
ArchiveName=Mary Jones
Zap=True

you need to replace 'kvsvault' with your EV server's name, replace EV site and Archive name would be affected archive. You can put multiple archive or all archive, following values can be put.

ALL (permissions are applied to all journal, shared, and mailbox archives in the specified vault site)
ALL_JOURNAL (permissions are applied to all journal archives)
ALL_SHARED (permissions are applied to all shared archives)
ALL_MAILBOX (permissions are applied to all mailbox archives)

Once you do that, in order see the changes, please REFRESH the vault admin console. Next time you synchronize the correct automatic permission should come from exchange. Please also have a look at below forum link.  

http://www.symantec.com/connect/forums/automatically-set-permissions