Throw an Error in an MSBuild Task

Question

How do you throw an error from within an MSBuild task and force the build to fail. Something like:

<Task>
  <ThrowError Condition="$(SomeCondition)" Message="There was a problem with the build" />
</Task>

Answer 1

Use the Error Task

<Error Condition="$(SomeCondition)" Text="There was a problem with the build" />

Answer 2

The Error-task would do the trick.

<Error
            Text="errormessage"
            Condition="errorcondition" />