In the Cubase 10.5.20 on Windows 10.
I was trying to import some multitrack files. I went to “File, Import”, and navigated to the location of my files, which is many sub-folders down on a drive, making the path name long.
When I clicked on a file in the folder Cubase immediately popped up the “Serious Problem” dialog.
If I copy those files to another folder with a shorter path name I can import without issue.