500 error after logging in

Hi. I suddenly started getting a 500 error while I was working on my blog 3 days ago. The login screen appears but none of the admin pages show up at all. The posts etc on my blog are all visible with no problems. It’s only everything from wp-admin downwards that’s affected. I’ve checked my error logs but I can’t seem to detect anything that started appearing at around the time the problem started. Right now the recurring error is :

[28-Nov-2007 09:16:23] PHP Fatal error: Call to undefined function: get_l_sidebar() in /home/menopau2/public_html/wp-content/themes/cutline-3-column-split-11/page.php on line 28

and this;

[Wed Nov 28 09:43:58 2007] [warn] Apache does not support line-end comments. Consider using quotes around argument: “# 11 hits”

Am totally at sea. Any help appreciated.