problems with file upload

hello, I am having problems with a site that I am setting up. basically the file uploads are not working at all. I know that it is not the script as they work elsewhere with no problems, What happens that when the form is submitted I can see the file going to the web server, but then nothing is happening on the web server, $_FILES is not being populated or any sign of the file. I am not sure where to go from here, how do I work out where it is failing. This seems to be happening before control is even being passed to the php script. I have tried turning all logging, but nothing is there. Any ideas, Thanks. The system is apache2 and php 4.3 Gordon.