Matlab linear correlation matrix in copularnd (copula random number) function

Consider we have 4 vectors, V1,V2,nf1 and nf2. We need to generate n=8736 random numbers that each pair of (V1,V2) , (V1,nf1), (V2,nf2) and (nf1,nf2) to be correlate as follow:

Rvv=0.6 for (V1,V2)
Rvn=0.5 for (V1,nf1) and (V2,nf2)
Rnn=0 for (nf1,nf2)

(It's not important what correlation of (V1,nf2) and (V2, nf1) is). Now we use copula to generate correlated random numbers in MATLAB:

    Rvv=0.6;
    Rvn=0.5;
    Rnn=0;
    n = 8736;

            %V1     V2     nf1      nf2
    Rho =   [1      Rvv     Rvn     0  ;    %V1
            Rvv      1       0      Rvn;    %V2
            Rvn     0       1       Rnn;    %nf1
            0       Rvn     Rnn     1 ];    %nf2

    Random_no = copularnd('Gaussian',Rho,n);

It's all OK when Rvv is 0.6, and Random_no will be a 8736 by 4 matrix, that each pair of columns are correlated as we specified by Rho Matrix. BUT when Rvv=0.9, MATLAB returns error as follow:

Error using mvnrnd
SIGMA must be a symmetric positive semi-definite matrix.
Error in copularnd 
u = normcdf(mvnrnd(zeros(1,d),Rho,n));

I can't understand what the problem is and how can I really generate correlated random numbers using copula. I'll really appreciate if anyone can help me through this problem.