We first discussed this problem in tip 2926 » The 'Work Offline' command is missing from the file menu?.
If you are using a local home page, the work offline command is unavailable. However, when you connect to an external site, it is still unavailable, until you start a new instance of IE?
There is a bug in Internet Explorer. It doesn't check/set the proper flags when you connect.
The only workaround is to start a new instance, by pressing CTRL+N or double-clicking the icon.