Help! Error message: Fatal error: Cannot redeclare win_is_writable() ...

Any suggestions on how to resolve this issue? Get below message on login. Site works fine for visitors.

Fatal error: Cannot redeclare win_is_writable() (previously declared in /home/burjoski/public_html/jwterrill.com/wp/wp-includes/functions.php:1588) in /home/burjoski/public_html/jwterrill.com/wp/wp-admin/includes/misc.php on line 554