ETS 6 Professional ( An Internal Error is Occured. Object reference is not set to an instance of an object)

Dear members . I got problem of launching ETS 6 professional software. I got error of (An internal error has occured. Object reference is not set to an instance of an object). Due to this error, I could not open the ETS 6 software. I tried to uninstall the ETS and reinstall again, but the same error still occured.How can I fix it?

TIA

Andrew