This is the first time i ever ran into this problem after installing a new ESXi host.  Added the host to our current vDS, moved into cluster and disabled maintenance mode.
Thought might be related to our newly upgrade 5.5, however seems a lot of people ran into same problem.

ERROR:

Migration to host failed with error Already disconnected (195887150).
vMotion migration [169942327:1389120124781890] failed writing stream completion: Already disconnected
vMotion migration [169942327:1389120124781890] failed to flush stream buffer: Already disconnected

vMotion migration [169942327:1389120124781890] socket connected returned: Already disconnected

VMware KB found on problem:
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1030267

I tried all the regular fixes:

• vmkping to and from the vmkernel port used for vmotion
• verify DNS
• restart the management agent on host given error.
• /etc/init.d/hostd restart
• /etc/init.d/vpxa restart
• Verified time on the both hosts
• Turned off Enable Migration in the Advanced Settings of the host and re-enabled it.
• vSphere web client -> Manage tab -> Settings tab -> Advanced System Settings
• Search for “migration”
• Find Migrate.Enabled and set to 0(disabled)
• Unchecked vmotion on the vmkernel port and re-enabled it.