no error code is reported in these circumstances as the next thing it does after undoing is to reboot to the usual log-in screen as if nothing has happened and Windows Update itself has lost all its history since my earlier attempts at installing this so I can't see an error code there either.
Are you sure? E.g. we were once shown that logging done by an install's WinPE was collected in a Panther directory. Also, (thanks to another recent incident) I just discovered that System Information's Windows Error Reporting section probably gets its data from Report.wer files stored here:
C:\ProgramData\Microsoft\Windows\WER\ReportArchive
They are much more readable that way than in msinfo32.exe.
There's more available via the Event Viewer too. Are you saying that all such diagnostics were wiped out somehow?
And of course, there may always be my favourite, ProcMon, to help guide us about what diagnostics are really available, how they correlate, and what they mean. <eg>
HTH
Robert