Microsoft.bcl.build.tasks.dll Is Used By Another Process //free\\ Jun 2026

This error occurs when Visual Studio retains a lock on the Microsoft.Bcl.Build.Tasks.dll

If using Visual Studio, go to and set maximum number of parallel builds to 1 . microsoft.bcl.build.tasks.dll is used by another process

Multiple projects trying to access the same BCL components simultaneously. This error occurs when Visual Studio retains a

Microsoft backported many of the "missing" features to .NET 4.7.2 and above. You generally do not need the Microsoft.Bcl.Build NuGet package if you are targeting .NET 4.7.2+. You generally do not need the Microsoft

If you cannot migrate, implement shadow-copying of the task DLL and enforce /m:1 in CI pipelines. For ephemeral build agents (Docker, Azure DevOps hosted agents), the problem often disappears due to clean state per build.

: Open Task Manager and terminate any running MSBuild.exe processes. MSBuild often stays active in the background (Node Reuse) to speed up future builds, which can maintain the lock. Clean and Manual Deletion : Close Visual Studio.