virtualbox.org

I'm getting this message after installing Office 2013 on Win7pro running
on top of Mint Linux 17.2 using Vbbox 5.0.2r102096.
Virtual m/c will not boot: it says that disk is full (and if it is I don't know
why - there is only Canon MX926 software and Office 2013Pro loaded).
The vdisk in 50GB, and should be < 50% full.

How do I resolve this issue?

"it says"? Please be clear whether the error message comes from your Linux host, the VBox software on the host, or the Windows guest. The exact wording would be good too, and/or a screenshot.

Check the space on the host partition where the VDI is located.