Attempting to Activate Cloner Generates a fatal error on a single blog install

I'm trying to install Cloner to move my site back and forth from my dev environment. This is just a single blog, not a Multisite install. When I try to activate the plugin I get the message :

Plugin could not be activated because it triggered a fatal error.

With the follow supporting information:

Fatal error: Call to undefined function is_subdomain_install() in /usr/www/virtual/<username>/<site_url>/wp-content/plugins/cloner/integration/integration.php on line 93

I cut out the username and site url because I know this is public and didn't want to compromise my site's security. I've specified an ftp server, username, and password in the wp-config.php file and confirmed that the username has sufficient privileges. I've also ensured that the file/directory permissions are correct. So can you help me out here? Thank you!