..."Undefined function is_front_page() in ....header.php

I am testing Atahualpa vsn 3.2 on WP vsn 2.3.3* on a functioning site with a static home page. The "other" theme is live right now...as I want people to look at my posts!!

When I test A, the (static page) home page, and all other pages work fine. Posts, however, give the fatal error. Help!

PS: Later versions of A won't load at all...dunno if this is my WP version, or plug-ins...and yes I did turn off all the plug-ins to see if they were causing the fatal error in 3.2...nope!

*Yes I will upgrade WP, then A, but because I also plan to change my theme (to A I love it...) am taking the moment to test A on my site http://yourfirstvisit.net first...I already run A on a different static page site http://WheretoFindHelp.org with a later version of both it and WP--works fine there...

From the WordPress codex

is_front_page()
When it is the front of the site displayed, whether it is posts or a Page. Returns true when the main blog page is being displayed and the 'Settings > Reading ->Front page displays' is set to "Your latest posts", or when 'Settings > Reading ->Front page displays' is set to "A static page" and the "Front Page" value is the current Page being displayed. Note: this tag was added at Version 2.5.

ergo, Atahualpa 3.2 requires a minimum of WP 2.5

Thanks--just donated. Would not have figured this out by myself...now I have to upgrade WP!! (gulp)