a few things to try to trouble shoot the problem?
add the following code at line 1 to make sure error reporting is turned on:
If there are other behaviors on the page that may redirect to another page, set them to not redirect.
on the bindings panel, expand the WA Upload Files Global Status and add the debug info binding to your page.
after testing an upload, post back any php errors that ay be reported and the results of the debug info along with a copy of your page so I can examine the code.