Exchange Creating Mailboxes For Pupils

Ive got a problem on Exchange that I need some help on please!!

Im trying to create mailboxes for our Year 9's and 10's. When the kids try to log on via OWA it prompts them for their username and password and will not let them in. If I as administrator log on to their mail boxes they are created successfully and after that the kids can log onto their own email accounts.

Any ideas?

Thanks.

I have seen this when creating new accounts and usually after 10 minutes or so it corrects itself.

Unfortunately this isnt the case as the accounts have been created for two weeks!

Tried IE7?

IE6 has a bug with authenticating users with OWA sometimes.

If not, try DOMAIN\username