Thanks for the reply but I solved it. When I calculated the power of the sources I didn't take into account the direction of the current relative to the polarity of the source. Doing that, I found that the total power of all sources is -38.88 W so the problem is solved.
Also I must apologize...
This is the circuit:
I have found all the currents and voltages with the Kirchoff's laws. I think they are correct because they perfectly matched the results of a QUCS simulation of the circuit.
I1 = -2.241
I2 = 0.759
I3 = -0.284
I4 = 1.957
I5 = -0.241
I6 = -1.284
V(R1) = I1*R1 = -2.241 * 1...