Our Intranet page has stopped working on some machines/some user accounts. The error I am getting points to a DNS issue but If I ping the site from the command line the it responds fine.

The error I'm gettting on IE is

Error: The web filter could not find the address for the requested site
Why are you seeing this:
The system is unable too determine the IP address of intranet.example.com

I'm not quite sure why it mentions the web filter as there is a proxy exception for the intranet page and if I run a trace route it doesn't go via the web proxy (filtering system).

Finally it isn't affecting everyone, just random users, also it doesn't affect the random users on all the client machines they use. I have one user where it happens on any client they log onto where most its just certian clients. It's even "fixed" itself for a few peoples.

EDIT: hey Mikey thanks for the fast response. Proxies are correct and automatic configuration is off (both via GPO)