MockServletContextManager doesn't exist in Seam 2.1 anymore.
Most likely you have an extra seam.jar 2.0.x in your classpath.
I see in jboss-seam-ui-2.1.0.GA.jar the class
I have checked my classpath and I haven't found any duplication.
I think my local maven repos messed up.
Redownloading the seam-ui.jar fixed my problem.
Thank you for the help.