If you own a Lumia 520, 525 or 526 smartphone and have yet to download the new 10051 build of the Windows 10 for phones technical preview, you will find that it is no longer available. Microsoft has pulled it from circulation for those devices due to problems with rolling back to Windows Phone 8.1.
A number of users who own those three Lumia models have reported those smartphones were bricked when they rolled back to Windows Phone 8.1. They were using the Windows Phone Recovery Tool after installing the Windows 10 for phones preview. A Microsoft rep has confirmed those reports on the company's support forums and added:
"We are pausing build availability for these devices temporarily while we investigate the issue and work with customers who have reported problems."
Microsoft released the 10051 build of the Windows 10 for phones preview last week, along with a list of known issues with the build.
Source: Microsoft Community; Thanks to iTroll for the tip!