Question: Error when evaluating integration of piecewise function

In the previous question, we discussed a workaround for evaluating a multi-variable integration. 

For the following example 

> g := (e1, e2, e3) -> piecewise(e1+1.200000000 <= e2 and e3-2.400000000 <= e1, evalf(64.00000000*exp((-1)*8.000000000*e1^2)*exp((-1)*8.000000000*e2^2)*exp((-1)*8.000000000*e3^2)/Pi^2), 0);
> 
> evalf(Int((x, y, z) -> g(x, y, z), [-2 .. 2, -2 .. 2, -2 .. 2]), 3);

Maple could start execution and do the computation.

However, when I tried the same example with different syntax, there are errors reporeted when the integration gets evaluated:

Case 1:

> a := [e1+1.200000000 <= e2, e3-2.400000000 <= e1];

> g := (e1, e2, e3) -> piecewise(a[1] and a[2], evalf(64.00000000*exp((-1)*8.000000000*e1^2)*exp((-1)*8.000000000*e2^2)*exp((-1)*8.000000000*e3^2)/Pi^2), 0);

> evalf(Int((x, y, z) -> g(x, y, z), [-2 .. 2, -2 .. 2, -2 .. 2]), 3);

Error, (in evalf/int) unable to store 'piecewise(e1+1.200000000 <= e2 and e3-2.400000000 <= e1, HFloat(6.484555753109632), 0)' when datatype=float[8]

Case 2:

> mu := 0:                                                                                                            

> sigma := 0.25:                                                                                                      

> elist := [e1, e2, e3]:                                                                                  

> E := Statistics:-RandomVariable(Normal(mu, sigma)):             

                                                    
> jointPDF := product(Statistics:-PDF(E, elist[i]), i = 1..3):

>f := evalf(jointPDF);

> g := (e1, e2, e3) -> piecewise(e1+1.200000000 <= e2 and e3-2.400000000 <= e1, f, 0) end proc

> evalf(Int((x, y, z) -> g(x, y, z), [-2 .. 2, -2 .. 2, -2 .. 2]), 3);

Error, (in evalf/int) cannot handle unevaluated name `e1` in evalhf

Here I couldn't quite understand the meaning of the error in each case. Did I miss anything here?