CRM2015 SDK:
This release of the Microsoft Dynamics CRM SDK for Microsoft Dynamics CRM 2015 and Microsoft Dynamics CRM Online 2015 Update is built on .NET Framework 4.5.2. You can use Microsoft Visual Studio 2012 or 2013 to build your managed code applications using .NET Framework 4.5.2 or later.
CRM2015的SDK必须在.Net Framework 4.5.2及以上版本上支持，但CRM2013只能最高选到4.5.1，安装了.Net Framework4.5.2还是选不到4.5.2为什么呢？
看提示：
| Tip |
|---|
| When installing .NET Framework 4.5.2 on your development computer, be sure to install the developer pack and not just the run-time. This will enable the 4.5.2 framework to be chosen in the New Project dialog box of Visual Studio and in the target framework drop-down menu of the project’s properties. |
安装了.Net Framewrok 4.5.2 run-time是不够的，需要安装developer pack，下面是下载地址：
http://www.microsoft.com/en-us/download/details.aspx?id=42637