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154 posts · Page 15 of 16

2026-05-12 errors csharp dotnet

Fix: System.IO.FileNotFoundException: Could not load file or assembly in a published app

Runs fine with dotnet run, throws after dotnet publish. The DLL is usually missing from the publish folder, not the runtime. Check deps.json, ProjectReference Private, and trimming.

2026-05-12 errors csharp dotnet

Fix: InvalidOperationException: Synchronous operations are disallowed

Replace the Stream.Read or Write call with ReadAsync/WriteAsync. As a last resort, set AllowSynchronousIO on Kestrel, IIS, or per-request via IHttpBodyControlFeature.

2026-05-12 errors csharp dotnet

Fix: RZ10012: Found markup element with unexpected name in Blazor

Blazor's Razor compiler emits RZ10012 when a PascalCase tag has no matching component type in scope. Add @using for the component's namespace in _Imports.razor, or @namespace in the component, then rebuild.

2026-05-11 errors csharp dotnet

Fix: dotnet ef migrations add fails with 'Unable to create an object of type DbContext'

EF Core's design-time tools could not instantiate your DbContext. Either expose a host via WebApplication.CreateBuilder, point to the right startup project, or implement IDesignTimeDbContextFactory.

2026-05-11 errors csharp dotnet

Fix: MSB3027 Could not copy X to Y. Exceeded retry count of 10. Failed

MSB3027 means MSBuild retried a file copy 10 times and a process still held the destination. Kill the locking process, exclude bin/obj from antivirus, or raise CopyRetryCount.

2026-05-11 errors csharp dotnet

Fix: The type or namespace name 'X' could not be found (after adding a project reference)

CS0246 right after a fresh ProjectReference is almost always a TargetFramework mismatch, a stale obj folder, or a missing using directive. Five fixes in order of likelihood.

2026-05-10 errors csharp dotnet

Fix: Cannot consume scoped service 'X' from singleton 'Y'

ASP.NET Core's scope validation throws this when a singleton would capture a scoped dependency for the rest of the process. Make the consumer scoped, or take IServiceScopeFactory and create a scope on demand.

2026-05-10 errors csharp dotnet

Fix: PlatformNotSupportedException: Operation is not supported on this platform in Native AOT

Native AOT strips the JIT and the interpreter, so reflection emit, expression-tree compilation, and unseen MakeGenericType throw at runtime. Find the call via IL3050 and replace it with a source generator or a pre-baked path.

2026-05-10 errors csharp dotnet

Fix: Unable to resolve service for type 'X' while attempting to activate 'Y'

ASP.NET Core throws this when a constructor asks for a type that was never registered, was registered on the wrong container, or was added after the host was built. Three concrete fixes cover almost every case.

2026-05-09 errors csharp dotnet

Fix: TaskCanceledException: A task was canceled in HttpClient

HttpClient throws TaskCanceledException for three different reasons: timeout, caller cancellation, or a connection-level abort. Tell them apart with InnerException and CancellationToken.IsCancellationRequested, then fix the right one.