Backup failing with 'Internal error'

This is the message I'm getting when trying to backup (on the step: taking snapshot):

When I check the link I see two possible causes:

You can get this error for 2 reasons:

1. There is too much data to be copied.
2. The original VM has been deleted and therefore backup cannot be taken. In order to keep the backup data for a deleted VM but stop the backup errors, Unprotect the VM and choose the option to keep the data. This will stop the backup schedule and also the recurring error messages.

First reason: What is 'too much data'?  This is an Ubuntu server and it's size isn't out of this world.  How can I backup this machine?  Is Microsoft actually saying that it isn't capable of taking a backup of certain virtual machines?  This is a Standard DS2 machine, no additional storage added.

Second reason: although I'm pretty sure that's not the reason since the machine is live whole the time and backups where going fine till the 26th when they suddenly stopped working.  I have completely unprotected and unregistered the server, deleted all backups and started over but I'm getting the exact same message.

/edit: backup and VM are both located in the same region.

/edit2: version is: WALinuxAgent-2.0.14 running on Ubuntu