My license.key file missing. How do I transfer the license to other servers?
The Craft .zip does not come with the license.key file. From the Craft docs: "It doesn’t get one until you have finished installing Craft and it has made its first call to our web service to check for updates."

Make sure your Craft edition upgrade went through, it seems a bit odd that you upgraded editions and you don't have a license.key file.

Double check that it's not there (craft/config/license.key), maybe by using a search tool on the whole Craft install.

Also try checking for Craft updates to see if that triggers the generation of a license.key file. Restarting the server may help, but you did say it was a production server so that might not be convenient.

If all else fails, I'm sure if you contact P&amp;T (support@buildwithcraft.com) they can sort it out.