Fatal Error on Upgradation to 3.2

Hi KevinB,
I upgraded my https://sakthidaran.learningprofessor.info/blog website to WordPress 3.2 version from Dashboard. It reported successful upgrade. But, when clicked return to dashboard the following error message appeared:
Fatal error: Call to undefined method WP_Scoped_User::WP_User() in /home/sakthi/public_html/sakthidaran/blog/wp-content/plugins/role-scoper/scoped-user.php on line 28

The site is not accessible. Kindly tell me how to sort out the problem. I can access scoped-user.php through cpanel. If any correction is required, I can follow your instructions.

Thanks in advance,

Sakthidaran