[Plugin: Digg Digg] Page won't load when Reddit button is enabled

If I enable the Reddit button, the page will not load, and I’ll get the following error in the log.

[22-Dec-2011 06:08:37] PHP Fatal error: constructNormalButtons() [function.constructnormalbuttons]: The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition “DD_Digg” of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition in /home/cnxtrans/public_html/cnxsoft/wp-content/plugins/digg-digg/digg-digg.php on line 105

http://wordpress.org/extend/plugins/digg-digg/