Error C407

I just received Error C407. The manual instructs, after receiving that error, to shut down Citavi and restart. I tried that but, upon attempting to restart, received another error message which I've copied and pasted below. What should I do next?

HTTP Error 500.30 - ANCM In-Process Start Failure Common solutions to this issue:

• The application failed to start
• The application started but then stopped
• The application started but threw an exception during startup

Troubleshooting steps:

• Check the system event log for error messages
• Enable logging the application process' stdout messages
• Attach a debugger to the application process and inspect

For more information visit: https://go.microsoft.com/fwlink/?LinkID=2028265

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Since posting this, I closed the box with the message above and Citavi restarted. However, it's now showing me an Error C415 message - i.e, that it's not possible to save to the cloud.

Edit to add further: After reopening Citavi, only my primary project is shown as an option. I had saved some backups and they used to show as options to open. They also do not appear under the file menu. The next issue is that after reopening, my "View" of Citavi had been altered, specifically the Categories column was no longer displayed. I was able to reopen and display it, but what the heck's going on?

Edit to add (2): Citavi will not allow me to save this project manually, either. When I click on "File", then "This Project", the option "Save a copy of this project" is grayed out.