Take a look in the server logs for any exceptions. I saw something similar when the jelly rendering of a plugin failed, the exception pointed me at the plugin which was ultimately caused by an upgrade failing leaving a mix of New and old plugin classes lying around.
-- You received this message because you are subscribed to the Google Groups "Jenkins Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to jenkinsci-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.