i18n problem

[leviathan]

Hello,
I used get simple in combination with the 'simple blue' theme, which requires i18n for navigation. However when I try to login with the plugins activated I get the following messages in debug mode. Without debug mode I get a white screen.

Code:

Warning: Cannot modify header information - headers already sent by (output started at D:\websites\***\admin\lang\nl_NL.php:1) in D:\websites\***\admin\inc\cookie_functions.php on line 23

Warning: Cannot modify header information - headers already sent by (output started at D:\websites\***\admin\lang\nl_NL.php:1) in D:\websites\***\admin\inc\cookie_functions.php on line 24

Warning: Cannot modify header information - headers already sent by (output started at D:\websites\***\admin\lang\nl_NL.php:1) in D:\websites\***\plugins\i18n_base\backend.class.php on line 7

I already read other topics about this problem but I can't find a solution. The workaround to go to the plugins.php after logging in works. But of course that is not a nice situation.

Thank you in advance for helping me!