form_tag_with_upload_progress with rails 2.x not updating its progress bar

Hello guys! I've just installed the upload_progress plugin and followed the instructions but the progress bar does not get updated.

When upload starts I can read "Upload starting..." just below the empty progress bar, when the upload completes it reads "Upload finished." and the progress bar turns all black.

What is really strange is that I have a lot of "Processing MyController#upload_status" in the log file.

Any idea on what might be wrong with this?

Thank you.