Why is a Matrix Not Invertible?

For our WNBA Massey Matrix model, some adjustments need to be made for a solution to our rating problem to exist and be unique.

To see this, notice that the following code produces an error:

> print(M)                                      
1  33 -4 -2 -3 -3 -3 -3 -3 -3 -3 -3 -3
2  -4 33 -3 -3 -3 -3 -2 -3 -3 -3 -3 -3
3  -2 -3 34 -3 -3 -3 -3 -4 -4 -3 -3 -3
4  -3 -3 -3 34 -3 -4 -3 -3 -2 -3 -3 -4
5  -3 -3 -3 -3 33 -3 -3 -3 -3 -3 -2 -4
6  -3 -3 -3 -4 -3 41 -8 -3 -6 -3 -2 -3
7  -3 -2 -3 -3 -3 -8 41 -3 -4 -3 -3 -6
8  -3 -3 -4 -3 -3 -3 -3 34 -3 -2 -3 -4
9  -3 -3 -4 -2 -3 -6 -4 -3 38 -3 -4 -3
10 -3 -3 -3 -3 -3 -3 -3 -2 -3 32 -4 -2
11 -3 -3 -3 -3 -2 -2 -3 -3 -4 -4 33 -3
12 -3 -3 -3 -4 -4 -3 -6 -4 -3 -2 -3 38

> solve(M)
Error in solve.default(M) : 
  system is computationally singular: reciprocal condition number = 3.06615e-17

Which of the conditions does \(M\) explicitly violate in this case?