When installing a Rollup, we recommend you use the same account that you used to install Exchange Server. If you are using a different account, that account needs to have Local Administrator rights as well as rights to read Active Directory on Exchange object as well as server level (as the update needs to determine which roles are installed on the server). Not having required permissions can lead to OWA not being updated correctly and displaying a blank page after update has completed.
If you have modified the logon.aspx file, it will not be patched by the Update Rollup installer. As a result Outlook Web Access may not be updated correctly and it may display a blank page after the update has finished. In order to avoid this problem, rename the logon.aspx file before applying the update rollup. After you apply an update rollup package, you must re-create Outlook Web Access customization in logon.aspx.
The update might take long time to apply. To try preventing this, follow the instructions in this post before applying the update. We are working on a permanent fix for this.