matlab-hfss api tool box

the code : % Create a new HFSS Project and insert a new design. hfssNewProject(fid); hfssInsertDesign(fid, 'testbox'); the error : ??? Error using ==> fprintf Invalid file identifier. Use fopen to generate a valid file identifier.

Error in ==> hfssNewProject at 36 fprintf(fid, 'Dim oHfssApp\n');