Question: Error, (in pdsolve/numeric/process_IBCs) initial/boundary conditions can only contain derivatives which are normal to the boundary,

Hello everyone,

I have a system of PDEs

restart:with(PDEtools):with(plots,implicitplot):

Pr:=1:A:=1:lambda:=1:Omega:=1:epsilon:=1:C1:=1:N:=5:b:=1:fw:=1:a:=1:

Eq1:=diff(f(eta,tau),eta,eta,eta)-diff(theta(eta,tau),eta)*diff(f(eta,tau),eta,eta)+

f(eta,tau)*diff(f(eta,tau),eta,eta)-(diff(f(eta,tau),eta))^2-(1+A*(1-theta(eta,tau)))*diff(f(eta,tau),eta)

+lambda*(1+epsilon*cos(Pi*tau))*theta(eta,tau)-Omega*diff(diff(f(eta,tau),tau),eta);

Eq2:=1/Pr*diff(theta(eta,tau),eta,eta)+f(eta,tau)*diff(theta(eta,tau),eta)-Omega*diff(theta(eta,tau),

tau);

sys:={Eq1,Eq2};

ICs := {f(eta,0)=0,theta(eta,0)=0};

bc:={D[1](f)(0,tau)=1+a*(1+A*(1-theta(0,tau)))*D[2](f)(0,tau)/C1,f(0,tau)=fw,theta(0,tau)=1+

b*D[1](theta)(0,tau),D[1](f)(N,tau)=0,theta(N,tau)=0};

pds:= pdsolve(sys,ICs union bc,numeric,time=tau,range=0..N);

The problem is with the bc D[1](f)(0,tau)=1+a*(1+A*(1-theta(0,tau)))*D[2](f)(0,tau)/C1. 

Any idea,

THanks