Error obtained while trying to run optistruct

Hi,

I am Nishanth and I am new to Optistruct , when I try to run my model in Optistruct I get an error. Can you please provide me with an optimum solution.

 

Objective of my topology optimization:

1. Maximizing the frequency of the component 

2. Minimizing the mass of the component.

 

I hereby attach the image of the error. Please suggest me a solution to my issue asap.

<?xml version="1.0" encoding="UTF-8"?>