Admin login and qTranslate

I have other two admins.When they want to log as admins, they can’t log into the dashboard directly.
I set debug on true and the errors are 15 times of “Notice: Undefined index: language in ……..public_html/wp-content/plugins/qtranslate/qtranslate_hooks.php on line 111”
One Warning: Cannot modify header information – headers already sent by (output started at //public_html/wp-content/plugins/qtranslate/qtranslate_hooks.php:111) in /home/ohsobell/public_html/wp-login.phpon line 384
An other Warning: Cannot modify header information – headers already sent by (output started at /homepublic_html/wp-content/plugins/qtranslate/qtranslate_hooks.php:111) in /home/ohsobell/public_html/wp-login.phpon line 396
What is the meaning of all of that?

http://wordpress.org/plugins/qtranslate/