Error 
is it possible to get negative hill yield coefficient(F,G,H,L,M,N) ? if possible then from that coefficients value the value of R in abaqus plasticity(http://c1260:2080/v6.14/books/usb/default.htm) potential section, showing this kind of error, I will be thankful to you if you kindly help me to fix this error.

Thanks in advance

F =2.69,G =2.45,H= -1.45,L=44.17,M=44.17,N=1.77

and the R value(http://c1260:2080/v6.14/books/usb/default.htm)

R11 = 1,R22 =0.8950,R33 = 0.4475,R12 =0.9214,R13=0.1843,R23 =0.1843