Cannot modify header information – headers already sent by

Hi,

I have installed the social polls by opinionstage Plug in and then closed my browser (firefox) without logging into an opinion stage account. Now I can not log in to the word press side (https://farbenstreit.de/wp-login.php) because the cookies for registration are blocked and I get the following lines (this happens on different computers (windows, mac, linux) and different browsers):

Warning: Constants may only evaluate to scalar values in /usr/www/users/punkt0/farbenstreit.de/wp-content/plugins/social-polls-by-opinionstage/plugin.php on line 53

Warning: Cannot modify header information - headers already sent by (output started at /usr/www/users/punkt0/farbenstreit.de/wp-content/plugins/social-polls-by-opinionstage/plugin.php:53) in /usr/www/users/punkt0/farbenstreit.de/wp-login.php on line 394

Warning: Cannot modify header information - headers already sent by (output started at /usr/www/users/punkt0/farbenstreit.de/wp-content/plugins/social-polls-by-opinionstage/plugin.php:53) in /usr/www/users/punkt0/farbenstreit.de/wp-login.php on line 407

Warning: Cannot modify header information - headers already sent by (output started at /usr/www/users/punkt0/farbenstreit.de/wp-content/plugins/social-polls-by-opinionstage/plugin.php:53) in /usr/www/users/punkt0/farbenstreit.de/wp-includes/pluggable.php on line 904

Warning: Cannot modify header information - headers already sent by (output started at /usr/www/users/punkt0/farbenstreit.de/wp-content/plugins/social-polls-by-opinionstage/plugin.php:53) in /usr/www/users/punkt0/farbenstreit.de/wp-includes/pluggable.php on line 905

Warning: Cannot modify header information - headers already sent by (output started at /usr/www/users/punkt0/farbenstreit.de/wp-content/plugins/social-polls-by-opinionstage/plugin.php:53) in /usr/www/users/punkt0/farbenstreit.de/wp-includes/pluggable.php on line 906
Farbenstreit

Also the first warning is shown on the webside.

Unfortunatly it is not my page and I normally just edit some page etc. but I have never edited the code, nor do I know how.

I would be super grateful for help. Thanks!!

The page I need help with: [log in to see the link]