Thanks for your post and apologies to hear that you are having an issue using TV Anywhere.
The first thing to try would be to delete the cache, cookies and browsing history within Internet Explorer. Once this is done, it's worth re-registering things just to keep it all refreshed.
Using a PC/Laptop go to anywhere.virginmedia.com > My Profile > Device Settings. Remove the current registration by clicking on the Delete button.
Once you've done this, using the device you are trying to re-register, open up the TV Anywhere page and log in. Try to stream Channel 4 from the On Now section and this should then prompt you to register the device.
Follow the prompts on the page and this will register the device for you and streaming will then commence