Apache Error

I have a reoccurring appearance of the following in my Apache’s error log that coincides with UpdraftPlus’s backup run. For example,

[Fri Aug 01 02:26:25 2014] [error] [client 162.144.85.142] exec used but not allowed in /home/mydomain/public_html/500.shtml

I am utilizing…
WordPress Version 3.9.1
UpdraftPlus Version 1.9.17
VPS hosted by HostMonster

While I typically run with a heavily-ruled .htaccess, I have confirmed that the error still occurs even with the vanilla WP-provided rules, which are:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

I have configured the backup files to upload to Google Drive.

Whenever I’ve checked, the contents of the backup files are valid.

Perusing my UpdraftPlus logs, I do not see any glaring errors.

I did notice that there is a .htaccess within the UpdraftPlus folder, containing the single line “deny from all”. Is this used to temporarily block site access while UdP does it thing? Might such an attempted file swap be the cause of my error log entries?

Thanks for your time.

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