> For the complete documentation index, see [llms.txt](https://docs.sannybuilder.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.sannybuilder.com/troubleshooting/errors/0039.md).

# 0039: Invalid element definition

The compiler can't read a mission or external script definition in the header. It may happen if either an id or label is missing or invalid.

**Possible solutions:** fix the definition:

```
DEFINE MISSION "0" at @label // error, integer id expected
DEFINE MISSION 0 at @label // OK
```