Problem uploading files (possibly an OS X issue?)

Hello,

I am implementing uploadify in my rails apps and I currently have a
similar problem as described in this old post
(http://www.ruby-forum.com/topic/156139) with the same error message.
This message occurs only when I try to upload a file when on a Mac and
the apps being deploued on my hoster environment (Apache+fastCGI).
Uploading from a windows environment works fine

Here is my configuration:
Development: Mac OS X.6, with rails 2.1.2, uploadify 2.1.4, webrick
--> everything is ok
Integration:
Mac OS X.6 on +flash 10 the client side and, rails 2.1.2+ Apache
2.2+fastCGI on the server side

I get this message only if I try to upload a file from a Mac, on a
windows platform it work ok.

Any idea on the solution?
Thanks in advance

Nicolas