Run the following tool to create a valid random machine key to place in your web.config or machine.config file.  This is beneficial in a webfarm where all of the server nodes need to have the same machine key, and it is also beneficial on a single box to keep the machine key consistent between IIS recycles and server reboots.  The top box provides the <machineKey /> tag while the bottom one shows its position in a simple web.config file.

  

MachineKey


MachineKey in web.config