Many may ask why would you need to do this? When upgrading from phpBB 2 to 3 the conversion does not keep the admin user you create. If your old admin user has an email address associated that no longer works or is accessible this makes it impossible to reset the admin password.
Some may just say "I'll just manually edit the e-mail address" but it won't work and phpBB will fail to find that user if you don't update the "user_email_hash" field but how do........
I spent so much time debugging this, most sites don't tell you a very important option to use with CURL and you will only find out this is the problem by running the PHP script from the command line you get the following output that shows the issue (I don't see any way to get this output from Apache itself).
* About to connect() to ip.ip.ip.ip port 25000
* Trying ip.ip.ip.ip... * connected
* Connected to ip.ip.ip.ip (ip.ip.ip.ip) port 25000
* succes........