Repeat what I said in  another thread:

Are you using python OpenCL (poclbm) in guiminer? If so, this problem has been happening for everyone in the last few days. See https://bitcointalk.org/index.php?topic=1334.msg732164#msg732164

Basically it shows that you are mining but the shares are not being submitted.
Anyway, the fix is coming up in Windows so just switch to Phoenix in guiminer or get cgminer for the time being. If you need direction for switching to phoenix, which is what I'm doing now, just ask.

BTW, I've also heard that using the older guiminer version works but have not tried this.