Error map
Cannot access a disposed context instance ObjectDisposedException: Cannot access a disposed context instance
.NET · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (12). 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 (12)
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) was never registered.
Blazor: An unhandled error has occurred. Reload 🗙
A Blazor component threw an exception; Blazor Server tears down the circuit (or WebAssembly logs to the console) and shows the re…
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.
DbUpdateException: An error occurred while saving the entity changes. See the inner exception for details.
SaveChanges failed in the database; the inner exception (SqlException/PostgresException) has the real reason — constraint violati…
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.
SignalR: Error: Failed to complete negotiation with the server / Failed to start the connection
The SignalR client couldn’t negotiate with the hub — wrong URL, CORS, authentication, or a proxy that blocks WebSockets/negotiate…
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…
HTTP Error 500.19 - Internal Server Error: The requested page cannot be accessed because the related configuration data for the page is invalid
IIS can’t read web.config — usually the ASP.NET Core Hosting Bundle (AspNetCoreModuleV2) or URL Rewrite module isn’t installed, o…
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…
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 LINQ expression 'x' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly
The query uses C# code EF Core can’t convert to SQL — custom methods, unsupported string/date functions, or complex projections.
Rust: error[E0502]: cannot borrow `x` as mutable because it is also borrowed as immutable
You tried to mutate a value while an immutable reference to it is still in use.
Two steps away (31)
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.
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.
UnsatisfiedDependencyException / NoSuchBeanDefinitionException: No qualifying bean of type 'X' available
Spring couldn’t find (or choose) a bean to inject.
CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views
Background code updated a View directly; UI changes must happen on the main thread.
WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?
A dialog or popup was shown with a context whose Activity is finishing/destroyed, or with the Application context.
ASP.NET Core: The CORS protocol does not allow specifying a wildcard (any) origin and credentials at the same time
The CORS policy uses AllowAnyOrigin() together with AllowCredentials(), which browsers forbid.
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 1062 (23000): Duplicate entry for key
An INSERT/UPDATE would create a duplicate value in a PRIMARY or UNIQUE key.
MySQL ERROR 1452: Cannot add or update a child row: a foreign key constraint fails
You inserted/updated a row whose foreign key value doesn’t exist in the referenced parent table.
PostgreSQL: ERROR: duplicate key value violates unique constraint
An INSERT/UPDATE would create a duplicate in a UNIQUE or PRIMARY KEY column — or the id sequence is behind the existing data.
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.
CORS Error: No 'Access-Control-Allow-Origin' header is present
The browser blocked a cross-origin request because the server’s response didn’t include the CORS headers allowing your site’s ori…
WebSocket connection to 'wss://x' failed
The browser couldn’t open (or keep) a WebSocket connection.
AmbiguousMatchException: The request matched multiple endpoints. Matches: X, Y
Two controller actions or minimal API endpoints have the same route and HTTP method.
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.
Windows Error 0x80070005 (E_ACCESSDENIED): Access is denied
Windows refused an operation because the account or process lacks permission — seen in Windows Update, installers, Task Scheduler…
InvalidOperationException: Collection was modified; enumeration operation may not execute
A list/dictionary was changed while a foreach loop was iterating it.
ASP.NET Core: The antiforgery token could not be decrypted / The required antiforgery cookie is not present (400 Bad Request)
Form POST failed antiforgery validation — the token is missing, the cookie is missing, or Data Protection keys changed so old tok…
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).
HTTP 413 Content Too Large (Request Entity Too Large)
The request body is bigger than the server is willing to accept — usually a file upload over the configured limit.
OAuth Error: redirect_uri_mismatch
The redirect URI in your OAuth request doesn’t exactly match one registered for the client in the provider’s console.
Kubernetes: CreateContainerConfigError — secret / configmap not found
Kubernetes can’t build the container’s configuration — usually a referenced Secret, ConfigMap or key doesn’t exist in that namesp…
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).
Rust: error[E0382]: borrow of moved value: `x`
A value was moved (ownership transferred) and then used again.
Rust: error[E0308]: mismatched types — expected `X`, found `Y`
A value’s type doesn’t match what the context expects — common with &str vs String, Option/Result vs plain values, and integer ty…
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