After activating the image backup for a client and starting a full image backup through the web interface, I get the following error message in the client protocol:
Could not read MBR Cannot retrieve master boot record (MBR) for the disk from the client.
After digging around a bit I noticed that the volume to image was not specified.
After entering volume C, the image backup started as expected.
I would suggest to adjust the error message for this case.
Server: UrBackup 2.4.11
Client: UrBackup 2.4.11