At startup the error occurs:
Object reference was not set to an object instance.
The error occurs when one of the XML control files is broken.
Solution: Delete control file GAEB-Online_2021_TreeLayout.xml!
Proceed as follows for the solution:
1.Open "Run" in Windows 10 with the key combination [Windows] + [R].
2.In the "Open" field, enter "%appdata%".
3.OK" opens the "Roaming" subfolder in the AppData folder.
4.There you will find the folder \GAEB-Online 2021 or \GAEB-Online 2021 USB, for example.
In this folder, delete the file:"GAEB-Online_2021_TreeLayout.xml".
If the file exists multiple times, delete it from all of the above folders.
Alternatively the command for the command line (CMD):
del "%appdata%\GAEB-Online 2021\GAEB-Online_2021_TreeLayout.xml"
Then restart the program.
Work with "GAEB-Online 2023 USB" and start the program directly from USB, then you will find the file you want to delete on the USB stick in the folder:
USB drive:\GAEB-Online_2021\GAEB-Online 2021\GAEB-Online_2021_TreeLayout.xml