We have been having some issues with some remote ESXi hosts that keep disconnecting for sometime now.  We have a ticket open with VMware and at this point they are stating that it is a bug and will be addressed in in upcoming patch.  VMware has no details as to when the patch will be released.  Paul found the following VMWare KB and we are going to test and see if it is at all related.

http://kb.vmware.com/selfservice/search.do?cmd=displayKC&docType=kc&externalId=1008643