WordPress is Subdirectory and .htaccess problems

Hey guys,
I got wordpress installed in a sub-directory (of root) called “blog”. At the root, I have my self-coded CMS running. The CMS interface displays a link called Blog, which simply links to http://mydomain/blog/.

Problem is whenever I try to access wordpress, I keep getting this message:

Fatal error: Call to undefined function wp() in /home/user/public_html/blog/wp-blog-header.php on line 18

I tried a lot of stuff, but can’t figure out why it refuses to work. But it’s pretty clear that it’s gotta be some path + file reading problem, which causes the wp-blog-header.php not be able to spot the wp() function.

Is this because of some .htaccess problem? Coz my CMS uses a htaccess similar to wordpress to generate pretty urls too..

CMS htaccess
————-
# Let the Script handle all pretty URLs
RewriteEngine On
RewriteBase /
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteCond %{SCRIPT_FILENAME} !-f
RewriteRule .* index.php [L]

WordPress htaccess
——————-
RewriteEngine On
RewriteBase /blog/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /blog/index.php [L]

As you can see there’s hardly any difference other than the RewriteBase.

Can anyone please throw some light on this issue?

Thanks a tonne,
m^e