Good Afternoon

I wonder if anyone can help me with a confusing problem I seem to be having...

Summary -

User changes Password on their laptop every month which syncs with the AD, which in line syncs with zimbra etc. After password change everything works fine for a random amount of time from 30 minutes up to 8 hours then the iPhone has a paddy and asks for a username and password.

Bit more Detail -

Our Zimbra syncs with our local AD running Windows 2008 R2 for the Gal and LDAP.

Every month our AD box requests the user changes his or her password which they normally then change straight away on their iPhone and other devices before Zimbra locks the account for trying too much using the old password.

Just recently our users have been doing the same as normal but after a random time, normally between 30 minutes and 8 hours the iPhone asks for the Password again for the account even though its been working for that amount of time. When the user puts the new password in as before it says its incorrect....

The weird thing is that you can try as many times as you like with the new password and the account never locks out as it normally would, but if you cancel the password request and have no mail for a while it just starts working again, this can be between 15 minutes and 2 hours from what I have heard.

The iphones are running the latest software (iOS 5.0.1)
Zimbra version is 7.1.2_GA_3268 on Centos 5.7

While the iPhones are having this issue mail still seems to work on both laptops and iPads....

Any Help would be great....

Hope it makes sense