My b2evolution Version: 4.0.3

I've upgraded to version 4.0.3 and I'm getting several errors, the most important at this moment:

Warning: Missing argument 2 for load_class(), called in /home/.../public_html/.../plugins/tweetmeme_plugin/_tweetmeme.plugin.php on line 23 and defined in /home/eduardot/public_html/literanova.net/inc/_core/_class5.funcs.php on line 86

Notice: Undefined variable: classname in /home/.../public_html/.../inc/_core/_class5.funcs.php on line 89

Warning: Cannot modify header information - headers already sent by (output started at /home/.../public_html/.../inc/_core/_class5.funcs.php:86) in /home/.../public_html/.../inc/_core/_template.funcs.php on line 59

Warning: Cannot modify header information - headers already sent by (output started at /home/.../public_html/.../inc/_core/_class5.funcs.php:86) in /home/.../public_html/.../inc/_core/_template.funcs.php on line 243

Warning: Cannot modify header information - headers already sent by (output started at /home/.../public_html/.../inc/_core/_class5.funcs.php:86) in /home/.../public_html/.../inc/_core/_template.funcs.php on line 244

Warning: Cannot modify header information - headers already sent by (output started at /home/.../public_html/.../inc/_core/_class5.funcs.php:86) in /home/.../public_html/.../inc/_core/_template.funcs.php on line 245

Warning: Cannot modify header information - headers already sent by (output started at /home/.../public_html/.../inc/_core/_class5.funcs.php:86) in /home/.../public_html/.../inc/_core/_template.funcs.php on line 246

I can get rid of this error messages if I turn off the tweetmeme plugin, but I don't want to. To be able for visitors to tweet my posts is very important to me.