Exchange 2007 SP3 OWA encounter the “reason=0” issue due to URLScan 3.1
Solution: uninstall URLScan 3.1 on E2K7.
The recommendation from Microsoft is NOT to run IIS Lockdown & URLScan on II6 and later version since there are similar builtin security configuration setting on II6 already.
HTTP Filter Settings for Microsoft Exchange Server 2007
Fine-tuning and known issues when you use the Urlscan utility in an Exchange 2003 environment
IIS lockdown and URLscan configurations in an Exchange environment
Exchange 2010 Security Guide
IIS 7.0/IIS6.0 – URLSCAN 3.1 and Outlook Web Access