You can get this error when installing a fresh Zimbra Desktop on your Windows PC if the association with the script engine is broken or has been changed by something else (like a text editor for modifying these files instead of running them).

The following fix works:
Run cmd.exe

Then run the following commands at the command line:

cscript.exe //H:WScript

and

regsvr32 %systemroot%\system32\vbscript.dll

If Zimbra desktop has partially installed use the installer to remove it and then reinstall a fresh copy and it should work properly now.