Thank you for your post.
Make sure you have the Extended Privileges turned on for fmphp. That is, open the database file, pull down the File menu and select "Manage -> Accounts & Privileges...". Click on the Extended Privileges tab, select fmphp and turn on the appropriate privilege sets. I would check every option to start. You can modify later.
It is also recommended that FileMaker Server is installed on a dedicated machine. You should also make sure IIS is running prior to configuration, and that the web server is set at default configurations prior to installation.
If you continue to have difficulty, please let me know.