Call to undefined function Guzzle\Service\Description\filter_var()

How to resolve this topic title error?
Backup file is created successfully, maybe.

[INFO] BackWPup version 3.0.10; WordPress version 3.5.1; A project of Inpsyde GmbH developed by Daniel Hüsken
[INFO] This program comes with ABSOLUTELY NO WARRANTY. This is free software, and you are welcome to redistribute it under certain conditions.
[INFO] BackWPup job: New Job; DBDUMP+FILE+WPPLUGIN
[INFO] BackWPup cron: 40 3 * * *; Fri, 3 May 2013 @ 10:43
[INFO] BackWPup job started manually
[INFO] PHP ver.: 5.4.7; cgi-fcgi; FreeBSD
[INFO] Maximum script execution time is 300 seconds
[INFO] MySQL ver.: 5.5.27-log
[INFO] curl ver.: 7.24.0; OpenSSL/0.9.8q
[INFO] Temp folder is: /usr/local/www/vhosts/*****/html/wp-content/uploads/backwpup-74611-temp/
[INFO] Logfile folder is: /usr/local/www/vhosts/*****/html/wp-content/uploads/backwpup-9a2f3-logs/
[INFO] Backup type is: archive
[INFO] Backup file is: /usr/local/www/vhosts/*****/html/wp-content/uploads/backwpup-74611-temp/backwpup_f008c8_2013-05-03_10-43-23.tar.gz
[03-May-2013 10:43:23] 1. Try to dump database …
[03-May-2013 10:43:23] Connected to database ****** on localhost
[03-May-2013 10:43:23] Dump database table “wp_commentmeta”
[03-May-2013 10:43:23] Dump database table “wp_comments”
[03-May-2013 10:43:23] Dump database table “wp_links”
[03-May-2013 10:43:23] Dump database table “wp_options”
[03-May-2013 10:43:23] Dump database table “wp_postmeta”
[03-May-2013 10:43:24] Dump database table “wp_posts”
[03-May-2013 10:43:24] Dump database table “wp_term_relationships”
[03-May-2013 10:43:24] Dump database table “wp_term_taxonomy”
[03-May-2013 10:43:24] Dump database table “wp_terms”
[03-May-2013 10:43:24] Dump database table “wp_usces_access”
[03-May-2013 10:43:24] Dump database table “wp_usces_member”
[03-May-2013 10:43:24] Dump database table “wp_usces_member_meta”
[03-May-2013 10:43:24] Dump database table “wp_usces_order”
[03-May-2013 10:43:24] Dump database table “wp_usces_order_meta”
[03-May-2013 10:43:24] Dump database table “wp_usermeta”
[03-May-2013 10:43:24] Dump database table “wp_users”
[03-May-2013 10:43:24] Dump database table “wp_yarpp_related_cache”
[03-May-2013 10:43:24] Added database dump “huhtikuujp.sql” with 2.79 MB to backup file list
[03-May-2013 10:43:24] Database dump done!
[03-May-2013 10:43:24] 1. Trying to make a list of folders to back up …
[03-May-2013 10:43:24] 143 folders to back up.
[03-May-2013 10:43:24] 1. Trying to generate a file with installed plugin names …
[03-May-2013 10:43:24] Added plugin list file “f11377a68c145cc0fc0c2aee63a8756c.pluginlist.2013-05-03.txt” with 2.42 kB to backup file list.
[03-May-2013 10:43:24] 1. Trying to create backup archive …
[03-May-2013 10:43:24] Compression method is TarGz
[03-May-2013 10:43:32] Backup archive created.
[03-May-2013 10:43:32] Archive size is 28.52 MB.
[03-May-2013 10:43:32] 2035 Files with 37.04 MB in Archive.
[03-May-2013 10:43:32] 1. Trying to send backup file to S3 Service …
[03-May-2013 10:43:33] Connected to S3 Bucket “*****” in ap-northeast-1
[03-May-2013 10:43:33] Starting upload to S3 Service …
[03-May-2013 10:43:49] Backup transferred to https://s3-ap-northeast-1.amazonaws.com/*****/*****/backwpup_f008c8_2013-05-03_10-43-23.tar.gz.
[03-May-2013 01:43:50 UTC] PHP Fatal error: Call to undefined function Guzzle\Service\Description\filter_var() in /usr/local/www/vhosts/*****/html/wp-content/plugins/backwpup/sdk/Aws/Guzzle/Service/Description/Parameter.php on line 212
[03-May-2013 10:43:50] ERROR: Call to undefined function Guzzle\Service\Description\filter_var()
[03-May-2013 10:43:50] Script stopped! Will start again.

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