Since a lot of time passed I am not sure on whether it is a good idea to add another post but I get the same error when starting up jboss-as-7.1.1.Final. Please find the log in the attachment.
After a restart of the server the problem did not show up again.
Does your application contain its own copy of the JBoss weld jar(s)?
If so, try removing them as this functionality is part of all JEE6 containers.
Oh, it did in fact. I removed it. Many thanks for the hint.