shading error when converted to VrayProxy

[Derek Forreal]

hi All,

 

i'm rendering a plan view of a garden design i'm working on but have noticed that there is a shading problem on the roof.

 

i have modelled the roof tiles as geometry and then converted to a VrayProxy. from the attachment you can see a clear shading error and i can't seem to find the problem (the attachment is part of a top-down view so the shading should be a simple even-shading - as it is it looks like the roof is kinked)

 

i have tried remodelling TWICE but upon conversion, the eroor shows in pretty much the same place. i have also tried cutting the original geometry in half and then converting but the error is still there. i f i render the original geometry only, then there is no problem but i need the memory so i can't afford to leave it in as 'normal' geometry.

 

any ideas what it might be?

 

TIA