I applied rolluppack 1 for Exchange 2010 on my test server and noticed that Outlook Web App was no longer functioning. As the Client access sever has still the self signed certificate i could get the warning when trying to access the website. But after pressing "continue annyway", only a blank page appears.
After uninstalling the rolluppack, Outlook Web App was functioning again. Reinstalled the rollup and yes, the issue returned. This proved that the update was causing the problem.
After running the UpdateCAS.ps1, the issue with Outlook Wab App seem to be resolved.
You can find the UpdateCAS.ps1 in the Bin folder in the Exchange Installation folder: Ussually C:\Program Files\Microsoft\Exchange\Bin\UpdateCAS.ps1.