Error when trying to import a product

[funinthesun]

Everytime I try to import a product I get this error: No file uploaded and no local file found.

I have run test file upload in Maintenance - Diagnostics and receive the following error: No file uploaded and no local file found. The test cannot continue.

The result looks like this:

Pertinent PHP Settings
file_uploads: On
open_basedir: /home/*****:/usr/lib/php:/usr/local/lib/php:/tmp
safe_mode: Off
upload_tmp_dir: None
upload_max_filesize: 16.00 MB

It was working fine before and no changes or alterations have been made to cause this problem? Does anyone know what might be wrong?

--------------- Added [DATE]1218989366[/DATE] at [TIME]1218989366[/TIME] ---------------

I have just tried to edit my header template and now I'm receiving this error:

Required variables have gone missing and execution can not continue. Please try again.

This error can sometimes occur as a result of Suhosin / Hardened PHP being installed on your server. If you know that you have Suhosin running and you have access to the PHP configuration, try increasing the value of the following variables:

* php_value suhosin.post.max_vars
* php_value suhosin.request.max_vars