Links not clickable in IE

[realfirst]

I'm working on this site http://zap3d.com/ and I have a problem: With Internet Explorer (IE) I can't click the two links (Upload and Download) but with Chrome and Firefox I can. Here is my CSS for Upload button\[code\]<a href="http://stackoverflow.com/User/Upload/" class="button_big upload_button"></a>\[/code\]\[code\].upload_button { position: absolute; left: 47px; bottom: 28px; width: 237px; height: 41px; border: none; background: transparent;}\[/code\]Thanks