"Automatic creation failed for user X" means that we couldn't make an account for that email address. This means that the account already exists on our system, so instead you will need to log in to the Cloudflare account, which you can do on the client side of WHMCS by clicking the "Setup Cloudflare" button.
Here's an example provisioning log:
2015-04-29 03:31:08 Cloudflare CNAME provisioning failed for hosting id: 17 2015-04-29 03:31:08 CNAME provisioning, server type: cpanel 2015-04-29 03:31:08 Automatic creation failed for user 3 2015-04-29 03:31:08 Account auto-create: email@example.com 2015-04-29 03:31:08 Zone isn't using Cloudflare yet. 2015-04-29 03:29:51 Deprovisioning example.com from Cloudflare failed, zone not found in WHMCS database. 2015-04-29 03:29:51 Deprovisioning example.com
Once you are on the Setup Cloudflare page you will need to log in to your matching Cloudflare account, and check any sites that you want to provision, after which the plugin will set everything up correctly.