Hi,
Looks like something went wrong with the server while it was updating. Probably it took too long and it threw an error, because scripts in PHP have a time limit when executing.
Anyway, login via FTP and remove the flexform folder from wp-content/themes/
WordPress should activate a default theme and you can proceed to installing the theme again (download the latest version from ThemeForest).
Note that this will not affect your content or theme options. But, if you made changes directly in theme files, those will be gone (they would have been anyway, if you updated from the dashboard).
Regards,
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Cosmin – Support