I was having similar problems, normally ending up with
a 'regsvr32' error - here's how I got around it - please
post a message if this worked for you (or not!)
Kevin
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Although I stopped all non-essential services before the
installion it appears that launching the SP4 installation
program (update.exe) starts the IIS Admin Service - after
launching the update program leave it in the
first 'Welcome' window for around 20 seconds, then check
the tasks that are running. If 'inetinfo.exe' is one of
them stop the IIS Admin Service again using the Windows
Service Controller.
Now continue with the SP4 installation and, hopefully, you
will have no ScriptMaps or regsvr32 errors. (Note inetinfo
will start during the sp4iis.exe installation part but
that is okay)