Installer for windows: Error "Couldn't load main class"

[pcm]

When running the Zimbra installer zdesktop_1_0_build_1593_win32.exe under Windows XP Professional SP2, I receive the following error:

Popup window title: "Error"
Couldn't load main class.
Log: c:\i4j_nlog_2

This happens when the install bargraph is about 3/4 complete, always after 610 files (69,882kB) have been written to a folder called, for example, "_dir5807" under the same folder as the .exe file.

The numeric part of that folder name is different each time I run the installer.

I cannot view the log file because it is "used by another person or program."
If I click on OK on the Error window, the log file disappears, and that temporary install folder is not deleted by the installer.

The same .exe install file installed with no problems on my other computer (Windows XP MCE SP3).

Any help would be greatly appreciated.