Microsoft .NET Framework error when exporting to LumenRT

I am unable to export a model to LumenRT because at 99% I keep getting this error. The model in question is a detailed equipment model imported to DGN from Parasolid format. I have tried dropping shared cells to geometry and solids to surfaces but that doesn't help either

Any ideas? I'd love to paste the full exception text but this forum keeps flagging my post as spam!

I'm running V8i SS3 on Windows 7. .NET version is 4.7