When downloading the latest Prism version and trying to compile in Visual Studio you might see an error like this:

"The property 'RegionManager.RegionName' does not exist in XML namespace 'http://www.codeplex.com/prism'"

There are number of suggestions and checks you can do here https://compositewpf.codeplex.com/workitem/10343, but in most cases this happens because files have been downloaded from internet and they are blocked by the OS.

You can fix this by editing the properties of the files or even easier go to your solution folder and run this powershell:

dir -recurse *.dll | Unblock-File