Debug This Error

Help me debug this error:

Language/Framework: {LANGUAGE}
Error message:
```
{ERROR_MESSAGE}
```

Code causing error:
```{LANGUAGE}
{CODE}
```

What I've tried: {ATTEMPTS}

Provide:
1. Error explanation (why it happens)
2. Root cause analysis
3. Step-by-step fix
4. Fixed code
5. Prevention tips
6. Related errors to watch for