We are getting below error when using 'Command file' button in Staad connect 21.03.00.146
You may try the solution explained here: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/37654/error-unhandled-exception-when-trying-to-open-the-editor-in-staad-pro-connect-edition
If that does not help, please upgrade to STAAD.Pro latest version - 22.00.00.15.
Answer Verified By: Dinesh Solanki