Crossing application boundaries

 I have a two asp.net applications structured as follows
root
-- app1
    --DirA
-- app2 (forms authentication)
    --Retrieve.aspx
I am trying to access DirA (I need the virtual path for DirA) from app2's Retrieve.aspx and I'm getting exceptions thrown when i use  app1/DirA as the virtual path (with request.mappath). What am I doing wrongly?
Thanks
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