I was still getting this issues too even with the latest plugin.
I was able to work around this issue by logging in to the advanced config panel at the URL <host>/wp-admin/admin.php?page=wponlinebackup§ion=advanced
From there I checked and selected Yes for use_wpdb_api and saved. I’m not sure if both checking the box and selecting Yes are necessary but I did both.
The database backups started working after that.
Info from my config:
Online Backup for WordPress Plugin Version 3.0.4
WordPress Version: 4.1.1 (standalone)
PHP Version: 5.5.9-1ubuntu4.7
Server Software: Apache/2.4.7 (Ubuntu)
MySQL Server Version:
MySQL Client Version: 1.0; MySQL Packet Size: 16?MiB
Memory: 256M; Post: 8M; Upload: 2M; Timeout: 30
Memory Changable: Yes; Admin Cache Size: 329.17?KiB
Status: 1 row, 27.79?KiB packet size, 226.49?KiB cache freed, 27.17?MiB memory used
Capabilities: hashcopy gzdeflate php5hash
End of Information
