error during powerflow run

[nilesh patel]

Dear Sir,  I am getting following error while i m running power flow of 
450 bus system. What could be the problem?
Warning: Matrix is singular to working precision. > In newtonpf at 
108  In runpf at 224 Warning: Matrix is singular to working 
precision. Newton's method power flow did not converge in 10 iterations.


Thanks.

Nilesh Patel