Thanks for posting!
It's requesting a username and password within the database that has the fmphp extended privilege enabled. You can check which one it's enabled for or enable it for the account you'd like by opening the database in FileMaker Pro and heading to File -> Manage -> Security. Once you're there, click on the Extended Privileges tab, select fmphp and then click Edit.
I have a followup questino regarding PHP pages generated by the PHP Assistant.
I see that the resulting PHP contains the user name/password in cleartext. Isn't this a security concern?
More specifically, I want to knwo what steps I need to take in a Windows 2k8 Server running FM10 Server. Should the "wwwroot" permissions be a certain way, or?