People Picker has stopped working

Hi,

I have a SharePoint 2007 farm where the people picker has stopped working on the portal web app. (I am posting this in the 2010 forum as I did not receive a response in the legacy forum). I am getting the following error in windows event viewer. Can someone tell me how to fix this issue? The people picker in Central Admin on the same farm is working, but not on this portal webapp.

thanks,

Sherazad