Hi Giannis
I am Dave, an Independent Advisor, I will help you with this . . .
That error is produced by the Cortana App, open the Settings App (gear icon on your Start Menu)
Go to Apps, then scroll down to find Cortana, select that and choose Advanced Options
Choose the Repair Option and then the Reset Option and then restart (not shut down) your PC
If the error still persists, download and install the latest version of Cortana form the Microsoft Store . . .