While developing your applications, OutSystems validates your implementation and issues errors and warnings, depending on the severity of the problem.
Both errors and warnings can occur at any stage of the module life cycle like implementing some logic, designing a screen, testing a query, or publishing to the server.
For most errors and warnings, double-clicking the error line in the TrueChange tab will take you directly to the source of the identified situation.
In OutSystems, an error is a problem that prevents deploying the module to the server.
Only when all errors are fixed, the module can be deployed to the server.
In OutSystems, a warning is a potential problem but does not prevent the deployment of a module to the server.
However, it's advisable to check the warnings and solve them, since they may be tip of the iceberg for unexpected or bad behaviours.