在进行潜类别分析时遇到了这个问题，分析数据包括四个二分类的变量，在进行1—3类别分析时没有这个问题，在进行四类别分析时出现的，想请教各位大神，这是什么原因？
     THE STANDARD ERRORS OF THE MODEL PARAMETER ESTIMATES MAY NOT BE
     TRUSTWORTHY FOR SOME PARAMETERS DUE TO A NON-POSITIVE DEFINITE
     FIRST-ORDER DERIVATIVE PRODUCT MATRIX. THIS MAY BE DUE TO THE STARTING
     VALUES BUT MAY ALSO BE AN INDICATION OF MODEL NONIDENTIFICATION. THE
     CONDITION NUMBER IS -0.220D-16. PROBLEM INVOLVING THE FOLLOWING PARAMETER:
     Parameter 19, [ C#3 ]
     ONE OR MORE PARAMETERS WERE FIXED TO AVOID SINGULARITY OF THE
     INFORMATION MATRIX. THE SINGULARITY IS MOST LIKELY BECAUSE THE
     MODEL IS NOT IDENTIFIED, OR BECAUSE OF EMPTY CELLS IN THE JOINT
     DISTRIBUTION OF THE CATEGORICAL VARIABLES IN THE MODEL.
     THE FOLLOWING PARAMETERS WERE FIXED:
     Parameter 16, %C#4%: [ OPA$1 ]
     Parameter 17, [ C#1 ]
     Parameter 18, [ C#2 ]