Backing Up a Boot Camp Partition
Backblaze will not back up any Boot Camp volume. The drive will be listed in Backblaze's "Select Hard Drives to Backup" as Boot Camp and will not be selectable.
The Boot Camp volume is formatted as NTFS, which Mac OS X can read but not write to. To back up that volume, you'll need to boot to Windows, install Backblaze for Windows and purchase a paid license for it.
Even if you have third party NTFS drivers to allow read/write of NTFS volumes, Backblaze will still disallow it to back up from Mac OS X. Since Backblaze is licensed per operating system installation, a Windows installation is considered an additional installation.
If you'd rather not purchase a separate license for your Boot Camp volume, because it has limited use, you can simply save or move important files to a volume that can be backed up from your Mac OS X installation - such as a FAT32 volume, or if you have Boot Camp drivers installed in Windows, to an HFS volume (since Apple's Boot Camp drivers allow read/write access to HFS volumes).