This isn’t exactly programming related, but it might trip up other people like it did to us.
In searching for a fix for this error, I ran across some good comments on the MS Exchange Team Blog for the rollup announcement. A few people posted the suggestion from MS PSS of running the update from within Powershell started as an administrator. I tried this and it did allow the update to run correctly and restored OWA functionality.
I haven’t seen any official comments on whether using Powershell is the new requirement for installing rollups. It might just be a UAC issue and need to be run as an Administrator, which isn’t possible without launching a new CMD or Powershell.