> 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/0203-to-0227.md).

# Runtime Core Errors

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

## Runtime Core Errors (0199-0228)

These errors occur in the core runtime functionality including scoping, observation, dirty checking, and computed properties.

* [AUR0199](/developer-guides/error-messages/0203-to-0227/aur0199.md) - Observing null/undefined
* [AUR0203](/developer-guides/error-messages/0203-to-0227/aur0203.md) - Null scope
* [AUR0204](/developer-guides/error-messages/0203-to-0227/aur0204.md) - Create scope with null context
* [AUR0206](/developer-guides/error-messages/0203-to-0227/aur0206.md) - Switch on null connectable
* [AUR0207](/developer-guides/error-messages/0203-to-0227/aur0207.md) - Switch active connectable
* [AUR0208](/developer-guides/error-messages/0203-to-0227/aur0208.md) - Switch off null connectable
* [AUR0209](/developer-guides/error-messages/0203-to-0227/aur0209.md) - Switch off inactive connectable
* [AUR0210](/developer-guides/error-messages/0203-to-0227/aur0210.md) - Non-recognizable collection type
* [AUR0217](/developer-guides/error-messages/0203-to-0227/aur0217.md) - Dirty check no handler
* [AUR0218](/developer-guides/error-messages/0203-to-0227/aur0218.md) - Dirty check not allowed
* [AUR0219](/developer-guides/error-messages/0203-to-0227/aur0219.md) - Dirty check setter not allowed
* [AUR0220](/developer-guides/error-messages/0203-to-0227/aur0220.md) - Assign readonly size
* [AUR0221](/developer-guides/error-messages/0203-to-0227/aur0221.md) - Assign readonly property from computed
* [AUR0224](/developer-guides/error-messages/0203-to-0227/aur0224.md) - Invalid observable decorator usage
* [AUR0225](/developer-guides/error-messages/0203-to-0227/aur0225.md) - Stopping a stopped effect
* [AUR0226](/developer-guides/error-messages/0203-to-0227/aur0226.md) - Effect maximum recursion reached
* [AUR0227](/developer-guides/error-messages/0203-to-0227/aur0227.md) - Computed mutating
* [AUR0228](/developer-guides/error-messages/0203-to-0227/aur0228.md) - Computed not getter


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