Hi Jack,
The Release Notes document for Visual COBOL for Eclipse 2.3 on Red Hat indicates that the space requirement during installation is only 3.69 GB, so this does not appear to be a space issue.
Are you able to (as root) manually create the parent of the target directory for the installation? You might try this using a command such as:
mkdir -p /opt/microfocus
If so, what does the df -h show on that directory?
Also, I notice that in another community post from this past March, it appears you successfully installed this same product on a Red Hat machine. Is this a different machine? Are you still installing a Personal Edition of the product?