Windows Phone 7.5 now compulsory to use Windows Phone Marketplace

Microsoft has announced that it has made Windows Phone 7.5 compulsory to download, buy, update or review apps in Windows Phone Marketplace. The change is now applicable in both phone/web-based stores.
Originally announced a month back, this change went live late yesterday and is gradually being rolled out worldwide.
If your Windows Phone is already running on version 7.5, then you won't notice anything different about the Marketplace. However, if you have an earlier version, you will start getting error messages.
To continue using your Windows Phone without any issues, make sure to update your phone to the latest version of software available. The detailed instructions on how to update Windows Phone devices are available at update central.