|If using SE ISAPI, the preferred way to configure the JVM Heap size is to use the SE Admin UI (and then cycle IIS). But if you configure the heap with invalid values then it is possible that IIS won't load SE the next time it initializes. "Service Unavailable" is a common response seen in the browser in this case.
The solution is to use a plain text editor such as Notepad to manually edit the file that contains the heap size settings. There are 2 possible files that could contain this information. Which one is used in your setup depends upon which Admin UI page you used (VM Settings Page -or- VM Options Page) in order to configure the heap.
For example VM Settings Page edits get written to:
C:\Program Files\New Atlanta\ServletExec ISAPI\ServletExec Data\VMSettings.pref (heap values in that file must be specified in Kilobytes)
VM Options Page edits get written to:
C:\Program Files\New Atlanta\ServletExec ISAPI\ServletExec Data\vmoptions.properties