The following simple problem gives the strange error message "The evaluated answer is not an answer hash : ||." There is also no answer shown under "Correct Answers".

```
DOCUMENT();
loadMacros(
"PGbasicmacros.pl",
"MathObjects.pl",
);
TEXT(beginproblem());
Context("Matrix");
$A = Value::Matrix->I(2);
Context()->texStrings;
BEGIN_TEXT
Enter the matrix \($A\). $PAR
Answer: \{ $A->ans_array(2) \}
END_TEXT
Context()->normalStrings;
ANS($A->cmp());
ENDDOCUMENT();
```

If I instead write $A = Matrix([[1,0],[0,1]]) or even $A = Value::Matrix->I(2) + Matrix([[0,0],[0,0]]), there is no error message, and the correct answer is shown correctly.

It seems there is something wrong with the encoding of the identity matrix, perhaps?