We recently uncovered a bug with Sharepoint file upload recording that may affect other file upload's as well.
The problem is that the IE events we receive in the recorder do not include any post data after the file upload parameter. To workaround this, the recorder parses the page and include all form fields after the file upload (uggh!). The problem then is that it records both the submit button and the cancel button, so when the sharepoint server gets the request it processes the cancel, not the submit. That's embarrassing. :(
To workaround this, simply delete the recorded cancel button from your post parameters.
With our new low level recording technology in Orcas we are able to get the right data and we have fixed this problem in Orcas Beta 2.