I was also geting the same error code 0x81000015 and disabled Carbonite. Does anyone know if there is a compatabilty issue with Backblaze?

Your anti-virus or compression program is interfering with the backup process. Try to run Disk Cleanup. The following procedure cleans up files associated with your user account. You can also use Disk Cleanup to clean up all the files on your computer. Try unassociating your compression program with Zip files and turning off your anti-virus while running the backup. You might need to set up Windows to use its internal boot manager. See if u have free space to backup. I want to be a MVP! | Computer Technician

Hi,Banmenau's suggestion is worth to perform. In addition, you can also refer to the following article:Windows 7 Backup Error: 0x81000015Thanks,Novak