SharePoint 2010 with Office Web APP , can't open word document

It is a SharePoint 2010 Server with Office Web App. All have latest service pack.

When user click on a Word document, they get a error message "Word Web App cannot open this document for viewing because of an unexpected error. To view this document, open it in Microsoft Word. <label class="WACErrorId" id="errorId">Error Id: cd73264a-fcc4-415c-bb6d-88188102044b, 20120210105531</label> "

I followed this post but no luck- http://social.technet.microsoft.com/Forums/en-US/officewebappssetup/thread/656b0744-c41e-4fb8-a289-1f6560c80148

Please help. Thank you.

-Neil