Issue: While installing Exchange 2013 CU5 you receive the following error message: “Setup can’t continue with the upgrade because the powershell has open files. Close the process, and then restart Setup.”
Solution: I didn’t have powershell running, and could not easily locate the process and didn’t want to start killing processes so I rebooted the server and then re-tried setup and the powershell error did not show up again. If you determine what process causes this, please post it in the comments. In the meantime, a reboot is all that is required.