The construction of the VS2013 F # project on Heroku fails with the project “Required attribute” “Import is empty”

I created an F # project using one of Nancy's templates in VS2013. The code is basically what created the template.

I can import the created .sln file into Xamarin studio and it all builds and runs without any errors or problems.

When I try to promote a project to Heroku, although I get an error:

/tmp/build_b3e2706f-20c8-421e-a1ce-781831880466/NancyFirstProject/NancyFirstProject.fsproj: error : /tmp/build_b3e2706f-20c8-421e-a1ce-781831880466/NancyFirstProject/NancyFirstProject.fsproj: The required attribute "Project" in Import is empty

I installed buildpack on Heroku as follows:

heroku config:set BUILDPACK_URL=https://github.com/aktowns/mono3-buildpack.git

I read that a similar error may occur if you update the project through VS2013.

Is the same error as me? Can I use another buildpack that solves this problem?

I think I can create a solution in Xamarin, but if possible, I would like to stick with vs2013.

EDIT: **

Just noticed this in the .fsproj file:

  <Choose>
    <When Condition="'$(VisualStudioVersion)' == '11.0'">
      <PropertyGroup>
        <FSharpTargetsPath>$(MSBuildExtensionsPath32)\..\Microsoft SDKs\F#\3.0\Framework\v4.0\Microsoft.FSharp.Targets</FSharpTargetsPath>
      </PropertyGroup>
    </When>
    <Otherwise>
      <PropertyGroup>
        <FSharpTargetsPath>$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)\FSharp\Microsoft.FSharp.Targets</FSharpTargetsPath>
      </PropertyGroup>
    </Otherwise>
  </Choose>
  <Import Project="$(FSharpTargetsPath)" Condition="Exists('$(FSharpTargetsPath)')" />