unable to update blog

Hey guy,
I tried a search on this issue but couldn’t find a thread that matched my issue.

I’ve been trying to update on of my WP sites to version 3.5.2 for several weeks now. whenever I do I get this error message:

Warning: require_once(/home/keyawin/public_html/wp-content/upgrade/version-current.php) [function.require-once]: failed to open stream: No such file or directory in /home/keyawin/public_html/wp-admin/includes/update-core.php on line 644

Fatal error: require_once() [function.require]: Failed opening required ‘/home/keyawin/public_html/wp-content/upgrade/version-current.php’ (include_path=’/home/keyawin/public_html/wp-content/plugins/google/lib/external/google:.:/usr/lib/php:/usr/local/lib/php’) in /home/keyawin/public_html/wp-admin/includes/update-core.php on line 644

what is the best fix. I’ve had trouble updating this site before.