This little tutorial should be applied only if you're running an ESXi 5.1 host with more than 32GB RAM.
If you're having less than 32GB RAM, you should use the Free License provided by VMware.

Starting with VMware vSphere Hypervisor 5.5, the limitation of 32GB RAM per server/host has been removed :) !

[cc lang='bash']
# Tested on VMware ESXi 5.1.0 build 1065491
\$ rm /etc/vmware/license.cfg
\$ cp /etc/vmware/.#license.cfg /etc/vmware/license.cfg
\$ /etc/init.d/vpxa restart
[/cc]