new user registration results in 403 error

*site url: zclientdev.net/coffee
*Joomla version: 1.5.22 with Quickstart package
*page that causes error: zclientdev.net/coffee/spice-a-fire/huevos-rancheros
*steps to cause error: 1) go to error page 2) click on login button 3) complete new user registration form 4) click on register button.

I have Joomla SEO enabled. This is a test site in development. It will eventually be transferred to its own domain.

Please advise on the registration error!!