HP 50g LINSO Linear Solver for System of Equations

[JDW]

My 50g is having trouble solving a system of linear equations which Wolfram Alpha solves very easily. On the 50g, I put the following 3 equations in an Array:

SQ(X)+SQ(Y)=5
Y=SQ(X)-3
X=Y+1

I then put the following into a second array:

X
Y

I then pressed WHT-LFT-ARROW & S.SLV, then pressed the LINSO soft key. It beeps a high-pitched tone and asks "Approx. mode on?" to which I answer YES. But it then coughs up the following error:

LINSOLVE Error: Not a linear system

Here's the Wolfram Alpha solution:

http://www.wolframalpha.com/input/?i=x%5...,x%3Dy%2B1

Why can't the 50g solve it?