Invalid path error creating directory?

The path where we would like to create a new directory is located:

../UserArea/invUploads/

Structure:

public_html (standard) -

• Site (where our DMX actions are stored, within this directory)
• UserArea / invUploads (the directory we want to create the new directory within)

Yet when we try to create the directory we see a path error:

"message": "Invalid Path! ../UserArea/invUploads/NEW"

Usually with PHP we would write around this with a small script but really, is that necessary? Is there any reason we can not create a directory in this location?

Bugging the &%$# out of us…

Any guidance appreciated!