System Reliability - Three components in parallel using FORM

Good Day,

Thanks for the amazing software (uqlab). I was trying to implement a system reliability problem of three components in Parallel using uqlab but get below error message.
Error Message:
Error using mvncdf (line 193)
SIGMA must be a square, symmetric, positive definite matrix.

Error in Systemrel (line 40)
Pf_FORM = mvncdf(-B, [0; 0; 0], R);

I have attached the MATLAB code and will greatly appreciate any help and advice on this .

SystemReliability .m (1.7 KB)