I had a host at version 5.1 that I upgraded to 5.5, and then to 6.5 update 1. For the 6.5 upgrade, I used the vCenter upgrade manager. First I had to remove some conflicting VIBs. The host upgraded and came up fine saying it's now on 6.5 build 5969303, but the vCenter upgrade manager still thought it was at 22%, and the host didn't reconnect.
I did the same thing yesterday with another host (with similar hardware) and it worked fine. The only difference was I did the upgrade from an SSH session instead of using the upgrade manager, since the vCenter is actually on that host. I did remove the conflicting VIBs.
With this newly upgraded host, I can connect via SSH, but none of the esxcli commands work. I get an error that says "Connection failed." I thought I'd try seeing if I could at least get the VMs started, but when I entered the command 'vim-cmd vmsvc/getallvms,' I got an error that said: "vim-cmd: error while loading shared libraries: libssl.so.0.9.8: cannot open shared object file: No such file or directory."