“opendir(/,/): Access is denied” when running a backup job

I get:

WARNING: opendir(/,/): Access is denied. (code: 5)

and

WARNING: opendir(/): failed to open dir: No such file or directory

Log:
[INFO] BackWPup 3.3.7; A project of Inpsyde GmbH
[INFO] WordPress 4.7.3 on https://www.mywebsiteurl.com/
[INFO] Log Level: Debug
[INFO] BackWPup job: Backup; DBCHECK+DBDUMP+FILE+WPEXP+WPPLUGIN
[INFO] Runs with user: (0)
[INFO] BackWPup no automatic job start configured
[INFO] BackWPup job started manually
[INFO] PHP ver.: 5.5.19 (32bit); cgi-fcgi; WINNT
[INFO] Maximum PHP script execution time is 300 seconds
[INFO] Script restart time is configured to 30 seconds
[INFO] MySQL ver.: 5.5.53-0ubuntu0.14.04.1
[INFO] Web Server: Microsoft-IIS/8.5
[INFO] curl ver.: 7.39.0; OpenSSL/1.0.1i
[INFO] Temp folder is: D:/inetpub/webs/mywebsiteurlcom/wp-content/uploads/backwpup-9bf830-temp/
[INFO] Logfile is: D:/inetpub/webs/mywebsiteurlcom/wp-content/uploads/backwpup-9bf830-logs/backwpup_log_9bf830_2017-03-13_11-23-22.html
[INFO] Backup file is: D:/inetpub/webs/mywebsiteurlcom/wp-content/uploads/backwpup-9bf830-backups/backwpup_9bf830_2017-03-13_11-23-22.zip
[13-Mar-2017 11:23:22] 1. Try to backup database …
[13-Mar-2017 11:23:22] Connected to database mywebsiteurl_com on 95.110.232.70
[13-Mar-2017 11:23:22] Backup database table “wp_commentmeta” with “0” records
[13-Mar-2017 11:23:22] Backup database table “wp_comments” with “0” records
[13-Mar-2017 11:23:22] Backup database table “wp_dps_modules” with “~13” records
[13-Mar-2017 11:23:22] Backup database table “wp_dps_modules_type” with “~2” records
[13-Mar-2017 11:23:22] Backup database table “wp_dps_page_as_img” with “~178” records
[13-Mar-2017 11:23:22] Backup database table “wp_dps_page_sort_order” with “~114” records
[13-Mar-2017 11:23:22] Backup database table “wp_dps_usage_stat” with “~15” records
[13-Mar-2017 11:23:22] Backup database table “wp_eg_grids” with “4” records
[13-Mar-2017 11:23:22] Backup database table “wp_eg_item_elements” with “1” records
[13-Mar-2017 11:23:22] Backup database table “wp_eg_item_skins” with “91” records
[13-Mar-2017 11:23:23] Backup database table “wp_eg_navigation_skins” with “17” records
[13-Mar-2017 11:23:23] Backup database table “wp_links” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_options” with “494” records
[13-Mar-2017 11:23:23] Backup database table “wp_postmeta” with “4465” records
[13-Mar-2017 11:23:23] Backup database table “wp_posts” with “1209” records
[13-Mar-2017 11:23:23] Backup database table “wp_revslider_css” with “109” records
[13-Mar-2017 11:23:23] Backup database table “wp_revslider_layer_animations” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_revslider_navigations” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_revslider_sliders” with “5” records
[13-Mar-2017 11:23:23] Backup database table “wp_revslider_slides” with “10” records
[13-Mar-2017 11:23:23] Backup database table “wp_revslider_static_slides” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_term_relationships” with “234” records
[13-Mar-2017 11:23:23] Backup database table “wp_term_taxonomy” with “36” records
[13-Mar-2017 11:23:23] Backup database table “wp_termmeta” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_terms” with “36” records
[13-Mar-2017 11:23:23] Backup database table “wp_usermeta” with “43” records
[13-Mar-2017 11:23:23] Backup database table “wp_users” with “1” records
[13-Mar-2017 11:23:23] Backup database table “wp_woocommerce_api_keys” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_woocommerce_attribute_taxonomies” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_woocommerce_downloadable_product_permissions” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_woocommerce_order_itemmeta” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_woocommerce_order_items” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_woocommerce_tax_rate_locations” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_woocommerce_tax_rates” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_woocommerce_termmeta” with “0” records
[13-Mar-2017 11:23:23] Backup database table “wp_wpmm_subscribers” with “~0” records
[13-Mar-2017 11:23:23] Added database dump “mywebsiteurl_com.sql” with 5,55 MB to backup file list
[13-Mar-2017 11:23:23] Database backup done!
[13-Mar-2017 11:23:23] 1. Trying to make a list of folders to back up …
[13-Mar-2017 11:23:23] WARNING: opendir(/,/): Access is denied. (code: 5)
[13-Mar-2017 11:23:23] WARNING: opendir(/): failed to open dir: No such file or directory
[13-Mar-2017 11:23:24] Added “wp-config.php” to backup file list
[13-Mar-2017 11:23:24] 889 folders to backup.