ALso the question is really old: This looks af if someone has moved the Allplan Directorys in Windows Explorer or removed the settings from Windows registry.

only help :
Search for the missing files. if the Folder is just "moved" to an other place, remove it to the correct subfolder (the path is shown in your picture)

or
reinstall the same Version. IF additonally to the Programm folder ( the Menue.bes is there also the Plugins) also the data Directorys got lost, the error message will change. Then you will need to search the latest backup ....