I'm working with a SharePoint 2010 deployment using Office Web Apps 2010, both RTM versions.
Web Apps works with all types of documents, with the exception of PowerPoint documents (both .ppt and .pptx files). When Web Apps tries to open the PowerPoint Documents, SharePoint prompts for authentication over and over again, but the document never opens.
I have checked both the Event Veiwer Application logs and the SharePoint Logs and I see no errors or anything else that might be the cause.