The BCL Build Tasks were designed for the old, complex .csproj format (pre-2017). Modern SDK-style projects do not use Microsoft.Bcl.Build at all.
If you are currently staring at this error and just need to push a build through, try these solutions in order of speed and effectiveness.
This also clears any corrupted file locks unique to that folder. microsoft.bcl.build.tasks.dll is used by another process
:
msbuild /t:Restore /p:RestorePackagesConfig=true msbuild /m The BCL Build Tasks were designed for the old, complex
Antivirus software often locks DLLs during the build process to check for threats. Add your project root folder (or the specific packages folder) to your antivirus to prevent interference. Technical Workaround: The "Pre-build" Hack
This prevents the tasks from executing during command-line MSBuild, bypassing the lock issue. This also clears any corrupted file locks unique
Have another persistent build error? Check our related guides on Could not load file or assembly and The process cannot access the file because it is being used by another process for similar locking issues.
The Microsoft.Bcl.Build package is stored in your solution’s packages folder. Deleting it forces a fresh restore.
