🟪 .NET errors

.NET runtime and ASP.NET Core exceptions.

CodeErrorWhat it means
FileNotFoundException assembly Could not load file or assembly 'X, Version=…' or one of its dependencies The runtime couldn’t find or load a referenced DLL — missing from the output, wrong version, or wrong platfor…
500.30 HTTP Error 500.30 - ASP.NET Core app failed to start IIS/Azure’s ASP.NET Core Module launched your app but it crashed during startup.
Sequence contains no elements InvalidOperationException: Sequence contains no elements / more than one element LINQ `First()`, `Single()`, `Last()` or `Max()` ran on an empty sequence (or `Single()` found several items).
InvalidOperationException InvalidOperationException: Unable to resolve service for type 'X' while attempting to activate 'Y' ASP.NET Core’s dependency injection container can’t build Y because one of its constructor dependencies (X) w…
JsonException object cycle JsonException: A possible object cycle was detected System.Text.Json found a reference loop (e.g. Order → Customer → Orders → …) while serialising, usually from…
NullReferenceException System.NullReferenceException: Object reference not set to an instance of an object Code dereferenced a variable that is `null` — the .NET equivalent of Java’s NullPointerException.