Dear Afia,
Sorry to hear that you encountered an issue with our legacy version. Please consider upgrading to our latest version PLAXIS 3D CONNECT Edition V21 as we do a lot of bug fixing and improvements with every release.
In order to be able to assist you with your project and identifying the reason for the problem you experience, please submit a service request.
Then, one of our support engineers can help you in detail: https://apps.bentley.com/srmanager/ProductSupport