Wordpress and mediawiki both throw error when trying to upload files

[AdamJ]

I'm using WP 2.9.2, MediaWiki 1.15.4, PHP 5.3.2 (cgi-fcgi), MySQL 5.1.32-community, on Windows WebServer 2008 with IIS7, and when I try to upload a file, I just get an internal error message like "Could not find file "C:\phpup\php[random characters].tmp"." I have uploads allowed in localsettings.php, the test uploads are small files (less than 100k), I have permissions Full Control for Everyone set for the C:\phpup directory. What else can I do?