Did you have FastCGI module installed on your machine before you installed the admin pack? If yes, can you check if you have following entry in your administration.config.
<add name="FastCgi" type="Microsoft.Web.Management.AdminPack.FastCgi.FastCgiModuleProvider, Microsoft.Web.Management.AdminPack.Server, Version=7.1.1.000, Culture=neutral, PublicKeyToken=1A5B963C6F0FBEAB" />
If not, try installing again. Choose custom and make sure FastCGI is selected in list of components which will be installed.