Error map
InvalidOperationException InvalidOperationException: Unable to resolve service for type 'X' while attempting to activate 'Y'
.NET · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (10). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (10)
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.
Angular: NullInjectorError: No provider for X!
Angular’s dependency injection couldn’t find a provider for a service/token the component needs.
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.
ObjectDisposedException: Cannot access a disposed context instance
Code used a DbContext after its scope ended — usually async void, fire-and-forget tasks, or capturing a scoped context in a singl…
dotnet ef: Unable to create a 'DbContext' of type ''. The exception 'Unable to resolve service for type DbContextOptions' was thrown while attempting to create an instance
dotnet ef migrations couldn’t construct your DbContext at design time.
UnsatisfiedDependencyException / NoSuchBeanDefinitionException: No qualifying bean of type 'X' available
Spring couldn’t find (or choose) a bean to inject.
EF Core: A second operation was started on this context instance before a previous operation completed
The same DbContext was used concurrently — async calls not awaited, parallel tasks sharing a context, or a context registered as…
JsonException: A possible object cycle was detected
System.Text.Json found a reference loop (e.g. Order → Customer → Orders → …) while serialising, usually from EF Core navigation p…
The dependencies of some of the beans in the application context form a cycle
Two or more Spring beans depend on each other through constructors, and Spring Boot 2.6+ forbids cycles by default.
InvalidOperationException: No authenticationScheme was specified, and there was no DefaultChallengeScheme found
[Authorize] triggered a challenge, but no authentication handler/default scheme is configured.
Two steps away (29)
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).
Fatal error: Unexpectedly found nil while unwrapping an Optional value
Swift force-unwrapped (`!`) an optional that was nil, crashing the app.
Fatal error: Uncaught Error: Call to a member function x() on null
Code called a method on a variable that is null instead of an object.
Angular: NG0100: ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked
A template value changed during the same change-detection cycle in which Angular already checked it (dev-mode only error).
Angular: NG8002: Can't bind to 'ngModel' since it isn't a known property of 'input'
The template uses a property binding that no imported directive provides — for ngModel, FormsModule isn’t imported.
Angular: NG8001: 'app-item' is not a known element — verify that it is included in the component's imports
The template uses a tag Angular does not recognise as a component — it was never imported (standalone) or declared/exported (NgMo…
HTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
Azure App Service: ":( Application Error" / container didn’t respond to HTTP pings
App Service started your app but it crashed or never listened on the expected port.
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 platform (x86/x64).
InvalidOperationException: No database provider has been configured for this DbContext
EF Core created a DbContext without UseSqlServer/UseNpgsql/UseSqlite — typically because the context was newed up manually or reg…
EF Core: The entity type 'X' requires a primary key to be defined
EF Core found an entity class without a key property it can recognise.
The instance of entity type 'X' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked
Two different objects with the same primary key were attached to one DbContext.
MySQL ERROR 1146 (42S02): Table 'db.table' doesn't exist
The query references a table that MySQL can’t find in that database.
PostgreSQL: ERROR: relation "x" does not exist
The table/view isn’t found — missing migration, wrong schema, or a case-sensitive quoted name.
MySQL ERROR 1022 (23000): Can't write; duplicate key in table
An ALTER/CREATE produced a duplicate key or constraint name — often a foreign key name that already exists in the database.
Web server failed to start. Port 8080 was already in use.
Spring Boot couldn’t bind its embedded server port because another process uses it.
Failed to configure a DataSource: 'url' attribute is not specified and no embedded datasource could be configured.
Spring Boot found JDBC/JPA on the classpath but no database URL.
Whitelabel Error Page — This application has no explicit mapping for /error
Spring Boot’s default error page — the request hit no controller mapping (404) or a controller threw (500).
HTTP 409 Conflict
The request conflicts with the current state of the resource — e.g. a duplicate or an edit based on an outdated version.
java.util.ConcurrentModificationException
A collection was modified while being iterated (even in a single thread).
HTTP 412 Precondition Failed
A conditional request header (If-Match, If-Unmodified-Since) didn’t match the current state of the resource.
RangeError: Maximum call stack size exceeded
A function called itself (directly or indirectly) too many times — usually infinite recursion.
java.lang.StackOverflowError
The thread’s call stack overflowed — almost always unbounded recursion, sometimes a bidirectional toString/equals/JSON cycle.
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.util.ArrayList` from Object value
Jackson found JSON whose shape doesn’t match the target Java type (object vs array, string vs number, missing constructor).
HttpMessageNotReadableException: JSON parse error / Required request body is missing
Spring couldn’t read the request body into your @RequestBody object.
MethodArgumentNotValidException: Validation failed for argument [0]
Bean Validation (@Valid with @NotNull, @Email, @Size…) rejected the request body.
Git: Permission denied (publickey). fatal: Could not read from remote repository.
SSH authentication to GitHub/GitLab/Bitbucket failed — no key, wrong key, or the key isn’t added to your account.
Azure AD (Entra ID): AADSTS700016 Application not found in the directory
The client ID in your sign-in request doesn’t exist in the tenant you’re authenticating against.
HTTP 401 Unauthorized
The request has no valid authentication credentials — you need to log in or send a valid token.
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