Image upload issues

I have tried the suggestions in the sticky above, including creating the .htaccess file, and I still receive an error saying “HTTP Error” when I try to upload images.

I contacted my server and they said that these two errors show up repeatedly in the php server log for my site:

[29-Mar-2008 15:46:03] PHP Fatal error: Call to undefined function image_downsize() in /home/.sites/111/site30/web/blog/wp-includes/post.php on line 2326

[29-Mar-2008 16:13:03] PHP Fatal error: Call to undefined function wp_constrain_dimensions() in /home/.sites/111/site30/web/blog/wp-admin/includes/image.php on line 173

I’m not sure what those mean, and am hoping someone can shed some light. Seeing as this blog is meant to be a photography blog, I really do need to be able to upload images! Everything else seems to be working fine.

Any help?