In SBS 2008, when you getting incomplete Microsoft Exchange Outlook Web Access sites. You will see Red X in place of images and the over-all theme will look off. This issue can also present itself as a blank screen when accessing https://remote.domain.com/owa. To resolve this issue install the latest Exchange 2007 Update Rollup. If it is already installed, the installation may be corrupt. In this case, you should reinstall the UR. At the time, the current UR is 8 which can be found here.
Source:→ SBS blog