When you attempt to install Enterprise Console 4.x, the installer stops at the 'Ready to Install' page, the 'Install' button is greyed out and you cannot proceed. The available space and required space are both shown as 0KB.
This is a known Windows installer engine issue.
Known to apply to the following Sophos product(s) and version(s)
Enterprise Console 4.5.0
Enterprise Console 4.7
Windows 2000 and above
What To Do
Re-run the installer. It should now install correctly.