> For the complete documentation index, see [llms.txt](https://docs.aurelia.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aurelia.io/developer-guides/error-messages/4100-to-4106.md).

# Validation Errors

Please see below a reference to each [@aurelia/validation](https://github.com/aurelia/aurelia/tree/master/packages/validation) package related error with explanations and resources for debugging and solving.

## Validation Core Errors (4100-4109)

These errors occur in the core validation functionality including rule serialization, deserialization, and rule provider operations.

* [AUR4100](/developer-guides/error-messages/4100-to-4106/aur4100.md) - Unable to deserialize expression
* [AUR4101](/developer-guides/error-messages/4100-to-4106/aur4101.md) - Rule provider no rule found
* [AUR4102](/developer-guides/error-messages/4100-to-4106/aur4102.md) - Unable to parse accessor function
* [AUR4103](/developer-guides/error-messages/4100-to-4106/aur4103.md) - Serialization display name not a string
* [AUR4104](/developer-guides/error-messages/4100-to-4106/aur4104.md) - Hydrate rule not an array
* [AUR4105](/developer-guides/error-messages/4100-to-4106/aur4105.md) - Hydrate rule unsupported
* [AUR4106](/developer-guides/error-messages/4100-to-4106/aur4106.md) - Hydrate rule invalid name
* [AUR4107](/developer-guides/error-messages/4100-to-4106/aur4107.md) - GroupRule no scope
* [AUR4108](/developer-guides/error-messages/4100-to-4106/aur4108.md) - GroupRule invalid execution result
* [AUR4109](/developer-guides/error-messages/4100-to-4106/aur4109.md) - Invalid rule execution result


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