# AUR4203

## Error Message

`AUR4203: {{controller}} is not of type ValidationController`

## Description

This error occurs when the validate binding behavior receives an object that is not a proper ValidationController instance. This typically happens when:

1. The validation controller is not properly injected
2. A different object is mistakenly passed as the controller
3. The controller instance is null or undefined

## Common Scenarios

```typescript
// ❌ Problem: Invalid controller type
export class MyComponent {
  controller = {}; // Not a ValidationController
}
```

## Solution

```typescript
// ✅ Correct: Proper validation controller injection
import { ValidationController, ValidationControllerFactory } from '@aurelia/validation-html';

export class MyComponent {
  validationController: ValidationController;
  
  constructor(controllerFactory: ValidationControllerFactory) {
    this.validationController = controllerFactory.createForCurrentScope();
  }
}
```