Project explorer Variable Configuration links.

I am trying to create a configuration variable link in Project explorer that points to a file one up from where my Dgn is found.

I have created a variable

A_WORKINGFILES = $(PARENTDIR(_DGNDIR))WORKING FILES

this works as expected with MS_REF_DEFAULTATTACHDIRECTORY = $(A_WORKINGFILES)

My problem is when I try to use A_WORKINGFILES in PE, the link fails to harvest.

How can I go one directory up in PE.

Adrian.