TextGen not found for 'jetbrains.mps.baseLanguage.math.structure.ComplexType

I'm trying to learn how to use MPS by following the book "The MPS Language Workbench", but I'm having trouble getting the first example to work in both MPS 3.4 and MPS 3.3.

I try creating a new solution project that uses the math language, and trying to create a new class like

public class HelloWorld {
  public static void main(string[] args) {
    complex a = 2 + 3 * I;
    System.out.println("hello");
  }
}

But when I try to run this program I get a number of errors, and the generated Java contains the line:

<!TextGen not found for 'jetbrains.mps.baseLanguage.math.structure.ComplexType'!>

And a similar thing for the use of I. I've tried searching to see if this is a common problem, but I can't figure out what I'm doing wrong or what I'm missing to make this work.

Any help would be appreciated,

Thanks