Buddypress not working with theme?

Hello,

I have mailed you about this issue before and I still wait for a fix. As soon as I turn on Buddypress on my site the whole admin palen will brake and I can not do anything. The error text that appears is the following:

Fatal error: Uncaught Error: [] operator not supported for strings in /customers/a/c/5/dreamon.nu/httpd.www/wp-content/plugins/buddypress/bp-activity/classes/class-bp-activity-component.php:281 Stack trace: #0 /customers/a/c/5/dreamon.nu/httpd.www/wp-includes/class-wp-hook.php(298): BP_Activity_Component->setup_admin_bar(”) #1 /customers/a/c/5/dreamon.nu/httpd.www/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters(NULL, Array) #2 /customers/a/c/5/dreamon.nu/httpd.www/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #3 /customers/a/c/5/dreamon.nu/httpd.www/wp-content/plugins/buddypress/bp-core/bp-core-dependency.php(143): do_action(‘bp_setup_admin_…’) #4 /customers/a/c/5/dreamon.nu/httpd.www/wp-includes/class-wp-hook.php(298): bp_setup_admin_bar(Object(WP_Admin_Bar)) #5 /customers/a/c/5/dreamon.nu/httpd.www/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters(NULL, Array) #6 /customers/a/c/5/dreamon.nu/httpd.www/wp-includes/plugin.php(515): WP_Hook->do_action(Array) #7 /customers/a/c/5/dreamon.nu/htt in /customers/a/c/5/dreamon.nu/httpd.www/wp-content/plugins/buddypress/bp-activity/classes/class-bp-activity-component.php on line 281

When this happen I need to delete the plugin via FTP to get access to the site again. Could you help me to solve this issue and activate the plugin for me? I have tried several times without fixing this problem and I dont know if I do something wrong or is it related to a bug?

My FTP: 
http://ftp.dreamon.nu

User: dreamon.nu

Pass: suomi78

Admin panel: 

http://www.dreamon.nu/wp-admin/

admin: admin78

Pass: suomi78

Thanks in advance.

Br,  mikael