Thrown on detecting an error communicating with the Sass embedded compiler: for example a badly formed or out-of-sequence message.

The payload is text describing the nature of the problem. There is probably nothing that a user can do about this.

Thrown on detecting a usage error of the Compiler API, for example trying to use it after shutdown.

Errors thrown for common SassFunction scenarios.

Generally these are thrown from your SassFunctions by SassValue family methods in response to error scenarios, for example a user passes a number where you expect a string, or a number in radians where you expected a length. Then the compilation fails, giving the description of the error as the failure reason.