when you say 'any other theme' have you tried more than just the facebook theme?
I know the facebook theme was developed very early in 1.8 and is a bit buggy on later builds judging by the comments I see going around.  Alternately redownload it, make sure it unzipped properly and uploaded properly.

i have tried Ultimate Cool Theme 2.0 and its also giving same error.

getting error when i active the theme

Fatal Error.
Redirect could not be issued due to headers already being sent. Halting execution for security. Searchhttp://docs.elgg.org/ for more information.

SecurityException Object
(
[message:protected] => Redirect could not be issued due to headers already being sent. Halting execution for security. Search http://docs.elgg.org/ for more information.
[string:private] => exception 'SecurityException' with message 'Redirect could not be issued due to headers already being sent. Halting execution for security. Search http://docs.elgg.org/ for more information.' in /engine/lib/elgglib.php:151
Stack trace:
#0 /mod/facebook_theme/start.php(382): forward()
#1 /engine/lib/elgglib.php(974): facebook_theme_index_handler('/dashboard')
#2 /index.php(17): elgg_trigger_plugin_hook('index', 'system', true, NULL)
#3 {main}
[code:protected] => 0
[file:protected] => /engine/lib/elgglib.php
[line:protected] => 151
[trace:private] => Array
(
[0] => Array
(
[file] => /mod/facebook_theme/start.php
[line] => 382
[function] => forward
)

[1] => Array
(
[file] => /engine/lib/elgglib.php
[line] => 974
[function] => facebook_theme_index_handler
[args] => Array
(
[0] => /dashboard
)

)

[2] => Array
(
[file] =>/index.php
[line] => 17
[function] => elgg_trigger_plugin_hook
[args] => Array
(
[0] => index
[1] => system
[2] => 1
[3] => 
)

)

)

)