wikiadmin export unable to create directory

I am trying to export my wiki collection using wikiadmin.

Running Server 5.1.7 on OS X 10.11.6

wikiadmin seems to be working OK (e.g .for listing wikis) but when I try to export the wikis I get an error relating to the creation of folders. Here is what I am doing / getting:

From a terminal account logged in as sudo (i.e. sudo -s)

bash-3.2# wikiadmin export -all -path /Users/administrator/Documents/wiki-export

Wikis available to export: 32

Using legacy format

exportPath=/Users/administrator/Documents/wiki-export

Error: Could not create folder at path /Users/administrator/Documents/wiki-export

Error: Exit with status: 9

The folder wiki-export exists, and the administrator account has full read / write access.

Any ideas what I can / could do to fix this would be gratefully received!

Thanks in advance for any help avail.