What is the actual problem? C3d crashes on the SAVEAS or QSAVE command? Nothing happens? It throws an error?
I've been using C3d since the Land Desktop days and can't remember having a problem saving a drawing.
What is the workflow from Pix4d? If you are building the C3d surface from DEM, it creates a separate file (.grs) that needs to be in the same folder as the .dwg. If you create a large TIN surface I believe the separate file is .mms.
