Fatal error and now cant even log into admin

Hi All:

I dont know what this means so I am pasting the message here in hope of solution:

Fatal error: Cannot redeclare bp_dtheme_ajax_querystring() (previously declared in /home/urbanshg/public_html/wp-content/plugins/buddypress/bp-themes/bp-default/_inc/ajax.php:20) in /home/urbanshg/public_html/wp-content/themes/custom-community/_inc/ajax.php on line 63

I just got the WP.MU premium install and started downloading cool plug ins I wanted and deciding on theme and them – BOOM – this fatal error message.

NOw I can’t log into admin/dash and have no idea what to think – please advise. Is this typical, did I somehow do something “wrong” to cause this collapse – how can I get back to my account. Im just wanting to know if this is user error on my end or something glitchy that needs worked out behind the scenes? Yikes – please H-E-L-P

I reeeaaallllyyy appreciate all who take the time to read this and respond!