This problem appears on some Windows 2008 installs, and appears to be due to the failure to load a particular control required by POP Collector.
On some systems, restarting the server resolves the issue. If it doesn't, I haven't yet found a solution. There are a couple of other threads on the subject on these forums, but as far as I am aware no-one else has been able to resolve this issue either. I have replicated it on a clean install of Win2k8, but still couldn't find any way of getting the problem component to properly register.