Question: Resolving NLPSolve errors

I am having some issues with NLPSolve (the code follows). As far as I can tell from the documentation, what is entered is syntactically correct.

with(Optimization)
[ImportMPS, Interactive, LPSolve, LSSolve, Maximize, Minimize, 

  NLPSolve, QPSolve]
nlc:={0<=d*(c-a) + c*(b-d), 0<=d*(c-e)+ c*(f-d), 0>=f*(e-a)+e*(b-f), (b-d)<=d*(c-a)+c*(b-d),(f-d)<=d*(c-e)+c*(f-d),(b-f)>=f*(e-a)+e*(b-f),(c-a)<=d*(c-a) + c*(b-d), (c-e)<=d*(c-e)+ c*(f-d), (e-a)>=f*(e-a)+e*(b-f),(c-a)+(b-d)<=d*(c-a) + c*(b-d), (c-e)+(f-d)<=d*(c-e)+ c*(f-d), (e-a)+(b-f)>=f*(e-a)+e*(b-f),2*(c-a)+(b-d)<=d*(c-a) + c*(b-d), 2*(c-e)+(f-d)<=d*(c-e)+ c*(f-d), 2*(e-a)+(b-f)>=f*(e-a)+e*(b-f)}

p:=2*(f-a)*(d-b) - [(d-b)*(c-a) + (d-f)*(e-c) + (f-b)*(e-a)]

NLPSolve(p,nlc)
Error, (in Optimization:-NLPSolve) non-numeric result encountered
 

Any help is much appreciated.