Just a few hiccups when upgrading to 5.1.0b... Nothing like the koolaid I had to mix up (here and here) to get from 5.0U1a to 5.0U1b to 5.1a.
I read the release notes and rebooted the VM at the end of the update.
Then nothing worked.
I logged into the console of the VM and saw that it had reverted to the temporary IP that I gave the appliance when I initially made the upgrade from 5.0 to 5.1. This may be due to the vApp options -> Properties still having the temp IP... I just changed it to the correct IP in /etc/sysconfig/network/ifcfg-eth0 (then ifdown eth0 / ifup eth0).
This worked for the main services, but not, it seems for SSO. I can't login to the web client, the error message clearly shows that it's trying to talk on the temp IP. I expect another reboot (or actually a shutdown/startup so that I can change the vApp settings) needs to happen for vmware-sso to start listening on the right address (restarting the vmware-sso did nothing).
/etc/vmware-sso/ls_url.txt shows the correct IP (lookup service)
/etc/vmware-vpx/vpxd.cfg did not. I restarted vmware-vpxd and still couldn't login.. a restart of the vmware-client service did the trick (and while it's called vmware-client, it did not quit active sessions with the C# client).
So I'm not sure if my editing of the vpxd file and the restart of vmware-client was needed or just the restart of vmware-client... at least this post will point someone in the right direction if they have the same issue.
The other fun thing was the ESXi hosts disconnected to vCenter and needed to be manually connected back. Not sure if this was because of the IP address change or something else.