[Typo3] Fatal error: Cannot redeclare class tx_sv_authbase in D:\WEB_NEW_Design\install_3_8_0\typo3\sysext\sv\class.tx_sv_authbase.php on line 165

[zsl vincent]

Hallo
      when i install the extension "Authentication Services (for 3.7) - 
cc_sv_auth" i have met a problem during the installation.
and then i can not log in to my typo3 site.everytime when i go to the site
"http://localhost/mysites/typo3"  there is a mistake displayed like that
"Fatal error: Cannot redeclare class tx_sv_authbase in 
D:\WEB_NEW_Design\install_3_8_0\typo3\sysext\sv\class.tx_sv_authbase.php 
on line 165" so that i can not login myself.
is there anyone who konws why that happen?