dns problem depending on user profile?

I have a weird problem…

I have a hosted website in a dmz zone. The local user where always able to visit www.example.com

Now SOME user are not able to visit www.example.com anymore. When entering http://192.168.2.x (local ip address of the server) the website opens in IE, but only the main page.

When logging on with a different account on the same computer, the website works.

The only thing that changed here is that we migrated our exchange server to microsoft online services.

Any ideas?