"Cannot load file or assembly" - Microsoft.Office.Interop.Excel

Question

I have a project targeting.Net 6.0 framework and I am trying to use Microsoft.Office.Interop.Excel as I would like to run an excel macro configured inside the.xlsm file that exists on the same local system. Regarding Excel version - I am running Microsoft 365 (I am not sure how this translates into Excel versions that used to be more explicit in the naming earlier). The error that I have when running my code is shown here:


This is the code where the problem occurs (last line basically):

void RunMacro(string macroFilename)
{
    Excel.Application xlApp = new Excel.Application();
    Excel.Workbook xlWorkBook;
   
    xlWorkBook = xlApp.Workbooks.Open(macroFilename);
    xlApp.Visible = true;

    xlApp.Run("Main");
}

For including Interop.Excel package in the project, I tried to install it as a NuGet package, so in that case the project file looks like this

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="DotNetCore.NPOI" Version="1.2.3" />
    <PackageReference Include="ExcelDataReader" Version="3.6.0" />
    <PackageReference Include="ExcelDataReader.DataSet" Version="3.6.0" />
    <PackageReference Include="Microsoft.Office.Interop.Excel" Version="15.0.4795.1001" />
  </ItemGroup>

</Project>

Alternatively, I tried to refer to the interop dll using the "Add project reference" option, so here is how the project file looks in that case:

 <Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="DotNetCore.NPOI" Version="1.2.3" />
    <PackageReference Include="ExcelDataReader" Version="3.6.0" />
    <PackageReference Include="ExcelDataReader.DataSet" Version="3.6.0" />
  </ItemGroup>

  <ItemGroup>
    <Reference Include="Microsoft.Office.Interop.Excel">
      <HintPath>..\..\..\..\..\..\Windows\assembly\GAC_MSIL\Microsoft.Office.Interop.Excel\15.0.0.0__71e9bce111e9429c\Microsoft.Office.Interop.Excel.dll</HintPath>
    </Reference>
  </ItemGroup>

</Project>

However, in the end, the error from the screenshot remains in both cases. What could be causing this? Thanks a lot for any help.

Answer 1

You need to have corresponding version of Office installed. It means for Interop version 15.0.0.0 you should have Office 2013 and other versions of Office will not work.