Could not be resolved because it has an indirect dependency on the assembly - Azure DevOps Build Pipeline

Question

I have two projects. Project 1 and Project 2. Project 1 refers to Project 2 in its csproj file. I have recently upgraded the Project 2 to a higher version of the .NET. When I did the same for Project 1 and ran my CI Pipeline, I have been getting quite a lot of errors, mostly like below. When I run the CI pipeline for Proj 2 seperately, it is building successfully.

I checked all possible places to see if I have any old references, but I am unable to find where exactly is the problem. Appreciate your help here.

Done Building Project "D:\a\1\s\dia-praj2\src\Proj-2\Proj-2.csproj" (default targets).
##[warning]D:\a\1\s\dia-proj1\proj1.metaproj(0,0): Warning MSB3274: The primary reference "D:\a\1\s\dia-praj2\src\Proj-2\bin\Release\Proj-2.dll" could not be resolved because it was built against the ".NETFramework,Version=v4.7.2" 

##[warning]D:\a\1\s\dia-proj1\proj1.metaproj(0,0): Warning MSB3275: The primary reference "D:\a\1\s\dia-praj2\src\Proj-2\bin\Release\Proj-2.dll" could not be resolved because it has an indirect dependency on the assembly "CsvHelper, Version=27.0.0.0, Culture=neutral, PublicKeyToken=8c4959082be5c823" which was built against the ".NETFramework,Version=v4.7" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.5".

##[warning]D:\a\1\s\dia-proj1\proj1.metaproj(0,0): Warning MSB3275: The primary reference "D:\a\1\s\dia-praj2\src\Proj-2\bin\Release\Proj-2.dll" could not be resolved because it has an indirect dependency on the assembly "Azure.Core, Version=1.22.0.0, Culture=neutral, PublicKeyToken=92742159e12e44c8" which was built against the ".NETFramework,Version=v4.6.1" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.5".

##[warning]D:\a\1\s\dia-proj1\proj1.metaproj(0,0): Warning MSB3275: The primary reference "D:\a\1\s\dia-praj2\src\Proj-2\bin\Release\Proj-2.dll" could not be resolved because it has an indirect dependency on the assembly "Microsoft.Bcl.AsyncInterfaces, Version=5.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51" which was built against the ".NETFramework,Version=v4.6.1" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.5".

My Build Pipeline

 a# ASP.NET
# Build and test ASP.NET projects.
# Add steps that publish symbols, save build artifacts, deploy, and more:
# https://docs.microsoft.com/azure/devops/pipelines/apps/aspnet/build-aspnet-4


pool:
  vmImage: 'windows-latest'

variables:
  solution: '**/Proj-1.sln'
  buildPlatform: 'Any CPU'
  buildConfiguration: 'Release'

name: $(Build.DefinitionName)_$(SourceBranchName)_$(Date:yyyyMMdd)$(Rev:.r)

resources:
  repositories:
    - repository: Proj-2
      name: Proj-2
      type: git
      ref: feature/Proj-2
# this is being defined in app-ci pipeline

steps:
- script: echo '$(Build.BuildNumber)'
  displayName: "echo build number"

- checkout: Proj-2
  displayName: 'checkout Proj-2'

- checkout: self
  displayName: 'checkout Proj-1'

- task: NuGetToolInstaller@1
  displayName: Install Nuget Package Manager

- task: NuGetCommand@2
  displayName: Restore Nuget packages
  inputs:
    command: 'restore'
    restoreSolution: '$(solution)'
    restoreDirectory: 'c:\packages'

- task: VSBuild@1
  displayName: Build dia-ui solution
  inputs:
    solution: '$(solution)'
    vsVersion: '16.0'
    msbuildArgs: '/p:DeployOnBuild=true /p:WebPublishMethod=Package /p:PackageAsSingleFile=true /p:SkipInvalidConfigurations=true /p:PackageLocation="$(build.artifactStagingDirectory)"'
    platform: '$(buildPlatform)'
    configuration: '$(buildConfiguration)'
    clean: true

- task: CopyFiles@2
  displayName: Copy everything to the Binaries dir
  inputs:
    Contents: '**/Prj1/abc/**'
    TargetFolder: $(Build.BinariesDirectory)

- task: ArchiveFiles@2
  displayName: Zip the binaries dir into a file called 'drop.zip'
  inputs:
    rootFolderOrFile: '$(Build.BinariesDirectory)/Prj1/abc/'
    includeRootFolder: false
    archiveType: 'zip'
    archiveFile: '$(Build.ArtifactStagingDirectory)/drop.zip'
    replaceExistingArchive: true

- task: PublishBuildArtifacts@1    
  displayName: Publish 'drop.zip' as an artifact
  inputs:
    PathtoPublish: '$(build.artifactstagingdirectory)/drop.zip'
    ArtifactName: 'drop'

Answer 1

The dependencies of your project do not match the .NET version your project is on now. I had the same issue and reinstalled the packages using the method mentioned here. In short: in the package manager console run update-package <package name> -reinstall

Do this for all packages installed in the project where you changed the .NET version.