Octave: "error: matrix cannot be indexed with . error: called from fitgmdist at line 486 column 14"

Question

I am trying to use the Gaussian mixture model to cluster my data in octave. As a start, I am trying to fit the data to a Gaussian distribution using the fitgmdist function in octave. However, I am getting the following error:

> (error: matrix cannot be indexed with . error:  
> called from fitgmdist at line 486 column 14)

whenever my source data gets bigger than a certain limit.

Attached below is a sample of the code I am using:

    clear; close all; clc
    pkg load statistics

    k = 30;                  % target number of clusters 
    X;                       % X is the input source data to be clustered 
    X_final = normalize(X);  % normalizing  the input data 

    gm = fitgmdist( X_final, k, 'start', 'plus',
                    'CovarianceType', 'diagonal',
                    'RegularizationValue', 0.0001
                  );