error: NU1100: Unable to resolve 'MicrosoftOfficeCore (>= 15.0.0)' for 'net5.0'

Question

In Terminal of Visual Studio Code, when I try to run:

dotnet add package MicrosoftOfficeCore --version 15.0.0

I get the following error on Visual Studio Code terminal:

error: NU1100: Unable to resolve 'MicrosoftOfficeCore (>= 15.0.0)' for 'net5.0'
error: Package 'MicrosoftOfficeCore' is incompatible with 'all' frameworks in project

Do anyone have an idea?

Dooryard

Answer 1

1. Try clearing the NuGet cache using dotnet nuget locals all --clear, and then try to add your package.

2. If that doesn't work, try deleting the NuGet.config file present inside C:\Users\<username>\AppData\Roaming\NuGet directory, and then restore it using dotnet restore command. Try adding your package after this.

The above solution works irrespective of whichever .NET version you're using.

Schoolboy

1. Same error 2. Works perfectly, thank you very much – Dooryard

Thanks a lot, we had the second problem with a fresh install of dotnet sdk 5.0.400. – Harbor

worked perfect, in my case <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" /> was missing as a package source in the default nuget.config created by the installation. – Chalybite

I had problem #2 from a net6.0 install using official scripted installer from learn.microsoft.com/en-us/dotnet/core/tools/…. same missing line as @Chalybite – Oxa

Got the error when creating a new webapi after installing .NET 7.0. Deleting the NuGet.config and "dotnet restore" fixed it. – Soap

Step number 2 fixed it for us, too. First step had no effect on our machine. – Tubuliflorous

Step #2 works, but dotnet restore may not work. In this case, simply re-run command you were trying to run. (e.g. dotnet install, dotnet add, etc.) Then, it will automatically add missing configuration as outlined by @Chalybite above. – Inglis

This bug is still present in VS Version 17.10.2. Step #2 worked for me. Step #1 did not. – Malign

Answer 2

You can check that whether you're having Nuget.config file in your root folder or not. If you don't have Nuget.config file, just create it and add the below code :-

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="NuGet" value="https://api.nuget.org/v3/index.json" />
    <!-- You can add additional sources as needed -->
  </packageSources>
</configuration>

Now, re-run the dotnet restore. This will definitely solve the error of NU1100

Herrah

Answer 3

Adding this in 2024 as a new answer (VS 2022, .NET 8/9 etc). It is possible that you have a packageSourceMapping element in your global NuGet.config causing this behavior.

I'm unsure how this element was added in my case, as the NU1100 error appeared globally while I was working on a project, where between builds it suddenly started throwing the NU1100 errors. Reverting changes had no effect.

The offending element may look something like this:

  <packageSourceMapping>
    <packageSource key="Local">
        <package pattern="Lula.Extensions.Xunit" />
      </packageSource>
  </packageSourceMapping>

The NU1100 error you get includes

the following source(s) were not considered: [...] nuget.org.

Full erroneous "default" config

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
  </packageSources>
  <packageRestore>
    <add key="enabled" value="True" />
    <add key="automatic" value="True" />
  </packageRestore>
  <bindingRedirects>
    <add key="skip" value="False" />
  </bindingRedirects>
  <packageManagement>
    <add key="format" value="0" />
    <add key="disabled" value="False" />
  </packageManagement>
  <packageSourceMapping>
    <packageSource key="Local">
        <package pattern="Lula.Extensions.Xunit" />
      </packageSource>
  </packageSourceMapping>
</configuration>

Fixed, proper default config

Using a config like the following should allow dotnet restore to work normally again. Note that you may have more legitimate package sources, but you shouldn't have a packageSourceMapping like above.

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
  </packageSources>
  <packageRestore>
    <add key="enabled" value="True" />
    <add key="automatic" value="True" />
  </packageRestore>
  <bindingRedirects>
    <add key="skip" value="False" />
  </bindingRedirects>
  <packageManagement>
    <add key="format" value="0" />
    <add key="disabled" value="False" />
  </packageManagement>
</configuration>

Notion