I have setup syncing on BlackBerry Z10 with active sync to our ISA Exchange 2003 server. It works but the device constantly promptes for the ActiveSync account password after 15 minutes. If Z10 is locked, I have to get the it working again by entering the user’s domain password for active sync. Try restarting, re-adding the account, but nothing happens.
The issue is caused with a timeout based authentication that affects the active sync. Windows 8 phone also has the same problem. Change the timeout for forms-based authentication will fix the issues.
Open the web listener of your ActiveSync rule, go to properties > Forms tab > Advanced, and uncheck “apply session timeout to non-browser clients”.