BEA WebLogic: Not able to connect to the Control Center

Symptoms

The Control Center cannot be opened.
This symptom is coming in two different flavors:

1. Desktop Instance

In Desktop for Web you see that the Desktop view gets a doubled menu bar when you try to open the Control Center.
The URL from the Control Center Connection of your Server object can be reached and returns a valid WSDL definition.
There will be an error message in the logs of the Desktop instance: java.lang.NoClassDefFoundError: com/ibm/wsdl/Constants at com.ibm.wsdl.xml.WSDLReaderImpl.parseDefinition.

2. Server Instance

When the URL does not work you will get a server error 500 when trying to connect to the Control Center of a VoiceObjects Server deployed in BEA WebLogic.
The Server instance seems to be running fine.
The SRV_Console.log shows the following message for each connection attempt: Web-service registration failed!
When I try to open the Control Center URL of the logical Server object in a web-browser I get an error 500 from BEA: java.lang.LinkageError: Class javax/xml/namespace/QName violates loader constraints

Resolution

The main cause for this issue is a version conflict between Java classes. BEA WebLogic contains some classes also used from VoiceObjects - and both can't co-exist in one JVM.

The solution is to remove the class from VoiceObjects.
To do this follow these steps:

1. Stop all nodes which host VoiceObjects instances - be it Server or Desktop
2. Remove the stax-api.jar from the /WEB-INF/lib/ folder of your exploded war file
3. Start all stopped nodes from 1. again.

Now the Control Center should work as expected again.