When opening a project you receive the following error message:
An unknown error occurred while opening the project. The internal error message is:
Failed to compare two elements in the array.
1. Close Citavi.
2. Locate the "ProjectCache" folder by copying the following folder path to the Windows Explorer address bar (screenshot):
%localappdata%\Swiss Academic Software\Citavi 6\
3. Rename the "ProjectCache" folder to "ProjectCache-BAK".
4. Start Citavi.
5. Open your cloud project.