UBB.threads PHP Forum Software Community Forums UBB.threads 7 Version 7 Support Error on backup inside the forum

If I try to use the option to backup from inside the forum:
Tools & Info -->Database Tools --> Backup Tables -->
and hit the (Click to test directory.) I'm getting this error:
Fatal error: Call to undefined function smartyPrepare() in /home/My_USER/public_html/forum/libs/html.inc.php on line 695

The folder I have there for backup is:
/home/My_USER/public_html/forum/admin/backup/
and it's 0744 permissions.

Version of Forum is 7.5.9
PHP Version 5.6.27

Could not find any mention to this error here.

If you have a large forum (a database over 100mb or so) you should not use the control panel backup tool, as you will likely hit the PHP Max Execution limit before your backup can be generated and fully downloaded; you should instead opt to backup your database via SSH (UBBWiki - Migration Guide [will show all of the commands needed to backup both your database and flat files; normally I'd link to the Backup Guide but it really needs to just include the portion from the migration guide]).

Using the admin tool you should take care to:
- Never backup to a folder that is web accessable; this is your database which includes user accounts and authentication details, basic security would mean you would make the backup to a folder UNDER the web root.
- The folder should be chmodded 777.

Have a quick read through this post -
https://www.ubbcentral.com/forums/ubbthreads.php/topics/255720/correct-way-to-handle-mysql-backups

From an older post, this is probably the same stuff, but its posted here also -
https://www.ubbcentral.com/forums/ubbthreads.php/topics/191156/how-do-i-backup-my-forums

Back to your original question though, It looks as though maybe your SQL Server became unreachable while trying to perform that action. Or it could be trying to access a table that is unavailable. You previously mentioned that you just upgraded from v7.4 to v7.5.9. A lot has changed between those builds. Go through the "Master Settings" section of your forum control panel, and confirm that all the settings are complete and are correct. Then attempt your backup again. In addition, as Gizmo mentioned above, if you have a huge database, the processing of that script could be timing-out, making the entire process prematurely quit. Gizmo mentioned to instead backup using the correct tools for such large databases.

Here's a link of a similar issue error message, which may not be related to your issue at all. But I'm posting it here for others who might find it useful.
https://www.ubbcentral.com/forums/ubbthreads.php/topics/167866/forum-upgrade-error