NuGet "error NU1100: Unable to resolve dependency" in CI

NU1100 is the umbrella resolution failure: restore walked the graph for a target framework and could not satisfy a dependency from any configured source. The message names the package and the TFM it failed for.

What this error means

dotnet restore fails with "error NU1100: Unable to resolve X (>= 1.0.0) for net8.0", often alongside a NU1101 or NU1102 for the same package.

dotnet

error NU1100: Unable to resolve 'Contoso.Lib (>= 2.0.0)' for 'net8.0'.

Common causes

No source provides the package for that framework

The configured feeds have no version of the package compatible with the project's target framework.

A missing or unreachable private source

The package lives on a feed that is not configured or could not be loaded, so resolution has nothing to draw from.

How to fix it

Confirm sources and framework support

Check that a feed hosting the package is in nuget.config.
Confirm the package supports the project's TargetFramework.
Re-run restore and read any paired NU1101/NU1102 for the precise gap.

Terminal

dotnet restore --verbosity normal

Align the target framework with the package

If the package only supports older TFMs, set a compatible TargetFramework or pick a version that supports yours.

Project.csproj

<TargetFramework>net8.0</TargetFramework>

How to prevent it

Keep nuget.config sources complete for every dependency.
Match target frameworks to what your packages actually support.
Use a lock file so resolution is validated before CI.