Hi,
There are some problems with flash uploader...
Some antivirus like AVG and ESET NOD32 integrate an HTTP traffic scanner...this create some problems while uploading files with flash uploader...(progress bar fire up to 100% immediatly and details for uploaded file wont be showed)...
More other antivirus are integrating this system...than it need a little trick...
See this page:
http://blog.formatlos.de/2008/10/21/filereference-upload-anti-virus-software/
Seems it simple need to check if there are the uploaded file and the size of uploaded file...this is a partial solution as you can read.
Thank