Backup failed - error code 4

On two separate computers, on two separate networks, I am having backups fail with error code 4.

Both computers are running Windows 8.1 x64.

Both have the same configuration:
Since Comodo Backup will not automatically backup to Comodo Cloud without asking for the username and password each time, I have Comodo Cloud mounted as a drive. I have Comodo Backup set to backup to that mounted drive of Comodo Cloud.

Every time Comodo Backup starts and tries to backup, it seems to get stuck at “Creating initial directory structure…” then I get error code 4. I do not know if this is related to the issue Comodo Cloud is having with the slow web interface or not, but the backup certainly is not working for me.