---
title: Troubleshooting
sidebar_position: 11
id: troubleshooting
license: |
  Licensed to the Apache Software Foundation (ASF) under one or more
  contributor license agreements.  See the NOTICE file distributed with
  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
  the License.  You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

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  distributed under the License is distributed on an "AS IS" BASIS,
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---

This page covers common C# runtime issues and fixes.

## `TypeNotRegisteredException`

**Symptom**: `Type not registered: ...`

**Cause**: A user type was serialized/deserialized without registration.

**Fix**:

```csharp
Fory fory = Fory.Builder().Build();
fory.Register<MyType>(100);
```

Ensure the same type-ID/name mapping exists on both write and read sides.

## `InvalidDataException: xlang bitmap mismatch`

**Cause**: The payload is not an xlang Fory frame, or it came from a peer/runtime mode that does
not emit the xlang header C# requires.

**Fix**: Ensure the payload was produced by an xlang-compatible Fory runtime. C# always expects the
xlang header and does not expose a separate `Xlang(...)` builder option.

```csharp
Fory writer = Fory.Builder().Compatible(true).Build();
Fory reader = Fory.Builder().Compatible(true).Build();
```

## Schema Version Mismatch in Strict Mode

**Symptom**: `InvalidDataException` while deserializing generated struct types.

**Cause**: `Compatible(false)` with `CheckStructVersion(true)` enforces exact schema hashes.

**Fix options**:

- Enable `Compatible(true)` for schema evolution.
- Keep writer/reader model definitions in sync.

## Circular Reference Failures

**Symptom**: Stack overflow-like recursion or graph reconstruction issues.

**Cause**: Cyclic graphs with `TrackRef(false)`.

**Fix**:

```csharp
Fory fory = Fory.Builder().TrackRef(true).Build();
```

## Concurrency Issues

**Cause**: Sharing a single `Fory` instance across threads.

**Fix**: Use `BuildThreadSafe()`.

## Validation Commands

Run C# tests from repo root:

```bash
cd csharp
dotnet test Fory.sln -c Release
```

## Related Topics

- [Configuration](configuration.md)
- [Schema Evolution](schema-evolution.md)
- [Thread Safety](thread-safety.md)
