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
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
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.