One issue i see is that you have bound the fi;le name setting to the Server File name binding that is created by the upload.
this is circular logic. you cant use the server file name variable for the file name setting since the file has not yet been created on the server.
the server file is a variable created by the upload after the file has been created on the server using any renaming settings you have set. In your case, you have set the if file exists to over write the existing file, but if you had selected to rename the new one with an increment value, this would need to get added to the files name.
in the upload settings, for the file name, you should leave the default value:
[FileName]
this will use the original file name when it saved the file on the server.
to trouble the file upload, make the following changes:
1) add the following code at line 1 to turn on error reporting:
<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>
2) add the following before the </body> tag:
<pre><?php var_dump($_FILES); ?></pre>
3) place you cursor in the body of the page, open the bindings panel, expand the WA UPloaded Files Global Status collection, select the Debug Info binding and click the Bind button at the bottom of the binding panel to add the debug info to your page.
once these changes are made, let me know and i will test the page to see the result and determine how to proceed.
