Opening as an Administrator didn’t fix the problem for me. What fixed it for me was opening both the .csproj and .csproj.user files and ensuring that both had UseIISExpress set to false.
In my case, the .csproj.user file was overriding the .csproj file even though SaveServerSettingsInUserFile was marked false.
<Project ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<UseIISExpress>false</UseIISExpress>
<!-- ... -->
</Project>