Exchange URL looping with siteminder portal

Issue: Customer called and complained of looping while accesing webmail via external OWA URL.
however, customers logs in ok when they type https://OWAexternalURL/owa
sytem configuration: Customer is running exchange 2007 scc cluster on windows server 2008. This issue started after migration to the exchange 2007 environment
Resolution: Customer didn't install all requirements needed to install exchange 2007 mailbox role on windows 2008. Specifically, basic auth, ISAPI extensions and windows auth weren't installed.
After installation, the problem was resolved