The error persisted even after I deleted CBRecaptcha and reinstalled CB 2.0.8, solution which solved the issue in the past.
It turned out that the problem was caused by an old language.php file, located in /components/com_comprofiler/plugin/language/default_language. I modified some messages in that file in the past and when I updated to CB 2.0.8 I replaced language.php with the modified one.
Now it works even with CBRecaptcha installed, the issue was in the language.php file.