Login problems

I recently did the WordPress updates to my blog. Since then, I have been unable to log into my blog – I’ve tried everything, including changing the password. No matter what I do, I cannot get logged in. I continue to be told that my user name or password are incorrect until I cannot try again for 20 min., then I keep getting the same error message –

Fatal error: Class ‘WP_Session_Tokens’ not found in /homepages/37/d113456392/htdocs/clickandbuilds/blog/wp-includes/pluggable.php on line 879

I have no clue what this means or how to fix it. I’m not very computer savvy about the technological stuff, so any help would be appreciated.

Thanks! Kathy

The blog I need help with is sewing-adventures.com.