Answer:
Find and delete the author.ini file on your new PC. Now, restart the Dlubal software (do not use the 2D icons), and carry out the activation process according to the attached instructions. The PC must be connected to the Internet at this time. If problems persist, please send me the authorization.txt file, which you can create in RSTAB/RFEM under Help → Authorization → Diagnostics (also possible in DEMO mode).