If an error occurs and the update is rolled back, the updating control in the browser will indicate that an error has occurred and the update has been rolled back, but the specific error will not be shown. If your update does not succeed, the cause can be determined by reviewing the update execution log file.
AppLife Update Action Log
If the update package was successfully validated, extracted, and executed, a log of the update process can be found in the Application Data folder of the user profile that executed the update. Using the update service, this will be the local system account. AppLife Update includes a log viewer that makes it easy to analyze update logs. To launch the viewer, select Log Viewer from the Tools menu. The log viewer will automatically display any updates executed under the current user, however updates applied by the web user (ASPNET, NETWORKSERVICE) will not be shown. To open these logs, choose to open an external log, and browse to the local system profiles, local appdata folder.
Windows 7 / Vista
C:\Windows\System32\config\systemprofile\AppData\Local\Kjs.AppLife.Update
Windows Server 2003
C:\Documents and Settings\NetworkService\LocalSettings\Application Data\Kjs.AppLife.Update
Windows Server 2008