[support] 304 Errors

I've just set up a local copy of a D7 site that works fine. On my local copy, the site seems to be fine until I try to get to the modules admin page (and now the Performance clear cache). When I go there, I get the beginnings of the overlay (graying out, etc.) but the page never comes up. There is nothing unusual in the Drupal error log, but the Apache log shows a 304 error. Given that the site never existed at this URL before, it can hardly be in the browser cache to be "Not modified."

Does anyone have any ideas? I've done several searches but found nothing useful. And, yes, I have dozens of other locals sites that work correctly.

Nancy

Injustice anywhere is a threat to justice everywhere. -- Dr. Martin L. King, Jr.