Thank you for your post.
When FileMaker Server 12 Advanced was first released some of the earliest license keys caused an issue with Custom Web Publishing and Instant Web Publishing working simultaneously. Based on this post and your previous post, you should contact technical support to have your license key checked and possibly exchanged.
Knowledge base article KB 299 has more information on this issue:
If you are in North America, please contact our Technical Support department toll-free at 800-325-2747. If you are outside North America, contact the FileMaker office nearest you.
If the key ends up not being the issue, let me know and we will discuss further troubleshooting steps.