Error: 'Target server is unavailable.' (NETIQKB5553)

fact
Exchange Migrator 1.x

fact
Exchange Migrator 2.x

symptom
Error: 'Target server is unavailable.'

cause

An invalid LDAP referral entry existed on the target Exchange server.

For more information regarding LDAP referrals please see the following Microsoft KB article:

195104 - XADM: Configuring an LDAP Referral Server in Exchange Server 5.5

fix
Remove or correct the LDAP referral entry, and wait for replication to occur.

Formerly known as NETIQKB5553