If I understand this correctly, all 4 hosts are managed by a single vCenter Server instance, and you can see/manage all VM's except the one you mentioned from vCenter Server, i.e. other VM's which are currently running on the 4.1 host are visible in the vCenter Server inventory?
In this case I'd reboot the vCenter Server to see whether this solves the issue. If this doesn't solve the issue the next step would be to restart the Management Agents on the 4.1 host. Both, restarting vCenter Server as well as restarting the Management Agents should not cause any issues with other running VMs, so unless you have other applications/services running on the vCenter Server you should not need to schedule downtime
André