Flash uploader logs out during “Crunching…” phase

After upgrading to 2.8, one of my blogs won’t let me upload any files via the Flash uploader. When I try to do so, I get a log-in prompt during the “Crunching…” phase, and so the file never gets uploaded.

– This problem only happens to one of my three blogs. All three of them are using 2.8, and all three of them have had clean installs (i.e. previous files were deleted and then reuploaded, didn’t use WP’s built-in upgrader)

– Although the log-in prompt pops up, WP itself doesn’t actually log out. If I close the media manager and go to another section of WP, for example, I am still logged in.

– I’ve upgraded to the latest version of Flash. I’ve tried using Firefox, Google Chrome, and even Internet Explorer. This problem occurs on all three browsers.

– The log-in window pops up for each individual upload I do. So for example, if I try to upload 15 images at once, I get 15 log-in windows in a row. If I log in to one of them, I get a “Are you sure you want to do this?” message. When I click the “Please try again” link, I’m taken back to the main page of the media uploader… where none of my files have been uploaded.

– Using the regular browser uploader works just fine; however, since that one blog happens to be a photo blog, you can imagine that I’d want to be able to upload more than just one file at a time. Thus, I’d really, really, REALLY appreciate it if I could use the Flash uploader again.

Any help on the matter would be greatly appreciated! Thanks!!