Vista - problems cleaning up news message history

I am not able to delete old news message headers and message bodies. When I
go to tools\options\advanced\maintenance\clean up now and select either
"remove messages" "delete" or "reset" nothing gets deleted. I get a pop-up
box asking me if I'm sure I want to delete the locally cached files. I select
"yes", I get another box that says "calculating message totals", then
nothing. All the headers and message bodies from the last year are still
there. Shouldn't they now be gone? What am I missing?