HFSS to CST exported file simulation problem

hi, I have CST 2008 and HFSS v11. CST 2008 supports transfer for HFSS files directly. but as earlier versions, it doesn't allow changes in the structure. I had memory shortage problems in HFSS so I tried running it on CST as CST handles memory problems in a better way. now when i export the file and run it, the simulation stops with giving error that either the mesh has zero volume or its too dense. I really can't figure out what i should do so that my simulation can run ok with reasonable accuracy (i.e. i don't have to vary mesh to decrease accuracy)

plz help me out.... thanks in advance