(maint) Fix faulty issue ILLEGAL_NUMERIC_PARAMETER and validation

There was a typo in the message that referenced a non existing variable.
This was undetected because there was no test to cover this.

When testing the expected behavior, it was found that the validation
was not correct as it allowed parameters to have hexadecimal names, but
not octal names. Now all numeric parameter names are disallowed (they
cannot be used or addressed anyway).