> 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/runtime-html/aur0503.md). # AUR0503 ## Error Message `AUR0503: Controller at is in an unexpected state: during activation.` ## Description Aurelia found a controller state outside the supported activation transitions. Activation normally starts from an inactive controller, while an already active controller needs no further work. The low-level Controller API does not queue a second activation requested during an active transition. Check any integration code that controls the controller lifecycle directly. It may have changed `controller.state` or called a controller method outside its lifecycle contract. If this occurs through standard routing or template composition, capture a minimal reproduction for the Aurelia team. ## What to Check * Find direct writes to `controller.state` and remove them. * Await the result of low-level `activate()` and `deactivate()` calls before starting unrelated controller work. * Record ``, ``, and the full stack trace. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.aurelia.io/developer-guides/error-messages/runtime-html/aur0503.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.