All applets and web start java applications has defaulted to high security since Update 11.
The security context that is used by vCO Client is set to high so some changes are needed within the Java control panel.

Resolution:

• Open the Java Control Panel
• Go to the Security tab. 
• At the bottom of the dialog you will see the current Exception Site List. 
• Click the Edit Site List button.
• In the exception entry dialog, enter the URL for your vCO Server