If you receive the error message "No vaild ESE KeyFile was found" check you have done the following:

1. Confirm your ESEkeyfile.xml file is in your ...tacticalops\system\ Directory
2. Make sure you open the ESE Account Manager.exe and go to 'Settings' and manually select the path of your tacticalops.exe file (this will then locate the Keyfile automatically)

If you do not know where the Keyfile has gone, disappeared, removed or deleted.. then try to make a new registration
You find out how to do so here: http://ese-protect.de/kb/

If you receive the Code 302, then I suggest you read here:
http://www.ese-protect.de/homepage/forums.php?m=posts&q=1056